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Three Decades of Repeated Absolute Gravity Measurements at the Finnish Antarctic Research

Station Aboa

JYRI NA

¨RA

¨NEN,

JAAKKO MA

¨KINEN,

MAARIA NORDMAN,

1,2

and ARTTU RAJA-HALLI

Abstract—Absolute gravity time series from Antarctica are

used to study the viscoelastic gravity change and deformation due

to Glacial Isostatic Adjustment (GIA) after the Holocene

deglaciation. Here we present the three-decades long absolute

gravity (AG) time series at the Finnish Antarctic Research Station

Aboa. A gravity increase of nearly 50 lGal is observed. Compar-

isons of the gravity trend with the land uplift observed in the Aboa

GPS station time series and with GIA model predictions show that

GIA can’t explain the observed gravity increase. We use satellite

gravimetry and altimetry, GPS measurements, and modelling to

interpret the gravity increase. A regional mass increase around

Aboa is observed with satellite gravimetry. Satellite altimetry

shows positive surface elevation change in the region over the last

three decades. GPS-based surface elevation change measurements

in the vicinity of Aboa also point to increase snow and ice volume.

Increased precipitation in Dronning Maud Land in the 2000s is

noted in the literature. Modelling of the direct attraction due to

added mass on the ice sheet around Aboa yields gravity change

comparable to what is observed in the time series. Consequently

the apparent explanation to the gravity increase is the positive mass

balance of the seasonal snow close to the gravity laboratory and of

the surrounding ice sheet. Increased direct attraction and elastic

ground deformation overshadow the viscoelastic GIA signal in the

absolute gravity time series. Conversely, absolute gravity time

series at Aboa can be used as an independent observation of the

mass increase.

Keywords: Antarctica, gravimetry, glacial isostatic adjust-

ment, mass balance.

1. Introduction

The purpose of the absolute gravity (AG) mea-

surements in Antarctica has been to study the gravity

changes due to Earth’s dynamics and to provide

reference values for relative gravity surveys as part of

the continental geodetic infrastructure. First AG

measurements in Antarctica were made in 1990

(Cerutti et al., 1992;Ma

¨kinen et al., 2007), soon after

transportable absolute gravimeters had become

available (Crossley et al., 2013). Finnish Geospatial

Research Institute FGI (then Finnish Geodetic Insti-

tute) was among the ﬁrst to measure AG in Antarctica

with ﬁrst measurements at the Finnish Antarctic

Research Station Aboa (Fig. 1) already in 1994. The

initial motivation for the FGI AG measurements in

Antarctica was to study the Glacial Isostatic Adjust-

ment (GIA).

During the last glacial maximum (LGM), the

Antarctic ice sheets were up to several hundred

meters thicker than today (e.g., Whitehouse et al.,

2012). Precise holocene deglaciation history of

Antarctic ice sheets is difﬁcult to construct due to,

e.g., sparsity of geological data (e.g., Noble et al.,

2020). Crustal loading and unloading by the ice

causes GIA (e.g., Martı

´n-Espan

˜ol et al., 2016), that

can introduce land uplift or subsidence depending on

the ice history. In addition to the GIA due to the

holocene deglaciation, the present day ice mass

changes also introduce elastic deformation of the

crust (Koulali et al., 2022). Understanding and

modelling GIA is essential for understanding the

Antarctic mass balance and subsequently its contri-

bution to sea level. GIA-model-based estimations to

the crustal response to ice mass (un)loading are

needed in the analysis of satellite-based gravimetry

Department of Geodesy and Geodynamics, Finnish

Geospatial Research Institute FGI, National Land Survey of Fin-

land, Vuorimiehentie 5, 02150 Espoo, Finland. E-mail:

jyri.naranen@nls.ﬁ; jaakko.i.s.makinen@gmail.com; maaria.nord-

man@aalto.ﬁ; arttu.raja-halli@nls.ﬁ

School of Engineering, Aalto University, Otakaari 4, 02150

Espoo, Finland.

Pure Appl. Geophys.

Ó2025 The Author(s)

https://doi.org/10.1007/s00024-025-03868-y Pure and Applied Geophysics

that is one of the most commonly used technique to

study the Antarctic mass balance (Gunter et al.,

2014). GIA models available for Antarctica have

large discrepancies in their predicted crustal move-

ment rates (Martı

´n-Espan

˜ol et al., 2016). Thus it is

valuable to provide geodetic in situ data that can be

used as an input in modelling and as a ground truth

for evaluating the model predictions.

Terrestrial absolute gravity measurements can be

used to study the mechanism behind the vertical

deformation of the crust due to, e.g., postglacial land

uplift (Bilker-Koivula et al., 2021) or variation in

contemporary ice load (van Dam et al., 2017). They

are complementary to and independent of the other

methods used to measure and study the crustal motion

and ice mass balance such as satellite positioning

(Buchta et al., 2025b), satellite gravimetry (Groh and

Horwath, 2021), and satellite altimetry (Nilsson

et al., 2022).

Since 1994 we have continued to measure abso-

lute gravity at Aboa station in seven measurement

campaigns. Duration of the measurements have var-

ied from 24 h to 2 weeks. When constructing and

analysing absolute gravity time series, it is essential

to understand the environmental changes that can

contribute to the measured gravity value. A particular

challenge for analysing absolute gravity time series in

Antarctica is that there are almost always large snow

and ice masses near the gravity measurement loca-

tions. Wind, precipitation, ablation, and other forces

are constantly changing the mass distribution of these

ﬁelds. This leads to changes in the measured gravity

(e.g., Breili & Pettersen, 2009). While the original

purpose of the repeated AG campaigns was to study

the viscoelastic gravity change due to GIA, it soon

became clear that other gravity-change signals

potentially overshadow the GIA signal. Besides the

elastic response of the crust to present day ice mass

changes, also the direct attraction due to mass chan-

ges in the seasonal snowpack close to the gravity

laboratory and changes in the mass of the surrounding

ice sheet needed to be assessed.

In this paper, we give a description and analysis of

the 30-year-long AG time series at Aboa, which is

one of the longest on the continent. Section 2gives

details of the data and methods used to analyse the

absolute gravity time series. Section 3reports the

results of our study and Sect. 4includes discussion of

our ﬁndings. Section 5summarises the main

achievements and the importance of our study.

2. Data and Methodology

In this section, we describe the gravity measure-

ments at Aboa, including both the absolute gravity

measurements and measurements made with a rela-

tive gravimeter. The latter are used to provide the

vertical gradient of gravity at the Aboa absolute

gravity station. In addition, we describe different

methods that we have used to understand the

changing mass environment around the gravity sta-

tion: GRACE satellite gravimetry, satellite altimetry,

GPS measurements, and snow height change mea-

surements with Real-time kinematic GPS (RTK-

GPS) method. GRACE provides monthly solutions

for regional (200?km scale) mass changes and

satellite altimetry regional scale understanding of the

snow and ice surface elevation change with impli-

cations to mass change. Three-dimensional ground

Figure 1

Gravity stations with repeated AG measurements in Antarctica by

the FGI are at the bases Aboa (Finland), Troll (Norway), Sanae IV

(South Africa), and Novolazarevskaya (Russia). Aboa is the only

station with more than two repeated measurement epochs. Single

measurements have been carried out at Maitri (India), Scott Base

(New Zealand) and McMurdo (USA)

J. Na

¨ra

¨nen et al. Pure Appl. Geophys.

movement values are obtained through continuous

GNSS measurements. RTK-GPS measurements have

been used to evaluate the snow surface change within

the closest 5 km of the gravity station. We start by

giving a description of the measurement location,

Aboa Station.

2.1. Aboa Station

The absolute gravity measurements reported here

have been taken at the Finnish Antarctic research

station Aboa (Figs. 1and 2). Aboa, a summer station

which is occupied annually for a few months by the

Finnish Antarctic Research Program (FINNARP)

expedition, is located in Western Dronning Maud

Land, East Antarctica. The station is built on a slope

of nunatak (mountain rising above the ice surface)

Basen rising approximately 200 ms above the sur-

rounding ice sheet. Basen, part of the Vestfjella

mountain range, is situated approximately 110 km

south of the edge of the Riiser-Larsen ice shelf and

15 km from its grounding line. The research station

area is basalt rock and regolith covered by varying

amounts of seasonal snow. The absolute gravity point

is at the geophysics laboratory at the station, which

provides a stable environment for the measurements.

The gravity point is on a concrete pillar anchored in

bedrock. The antenna of the Aboa GPS station,

labelled ABOA, is also attached to bedrock and

located approximately 20 ms from the geophysics

laboratory. The coordinates for the gravity point are

732037.5900 S, 1324023.9800 W (ITRF97). The

height of the gravity point is 462 ms above sea level.

2.2. Absolute Gravity Measurements

The absolute gravity measurements at Aboa

Station were started with the JILAg-5 instrument

(Faller et al., 1983) in 1994 and repeated in 2001. In

2004, in the 2005/2006 season, and in 2012 FG5-221

Figure 2

Satellite image of the Basen nunatak with elevation contour lines for the surrounding ice sheet. The width of the image is 40 km. Image

produced with Quantarctica 3 (Matsuoka et al., 2018) using Landsat Image Mosaic of Antarctica (LIMA, https://lima.usgs.gov/) background

and contour lines from Bedmap2 (https://www.bas.ac.uk/project/bedmap-2)

Three Decades of Repeated Absolute Gravity

was used (Niebauer et al., 1995) then in 2017, 2020,

and 2024 FG5X-221 (Niebauer et al., 2011), which is

currently the state-of-art instrument for absolute

gravity measurements. All these instruments have

been used as the national metrological standard for

the acceleration of free fall in Finland. Starting in

1989 (Boulanger et al., 1991) they have participated

in the international and regional comparisons of

absolute gravimeters; the latest reports are Newell

et al. (2024) and Wziontek et al. (2025). This gives us

valuable reference for the performance and accuracy

evaluation of the instruments. A listing of all the

comparisons where our gravimeters have participated

until 2021 and their results is found in Bilker-Koivula

et al. (2021).

Results from AG measurements at Aboa in 1994

and 2001 with the JILAg-5 and in 2004 with the FG5-

221 were previously published by Ma

¨kinen et al.

(2007). All the measurements since 2004 have been

acquired and post-processed with the ‘‘g’’ software

(Micro-g LaCoste Inc., 2012) from the manufacturer

of the instruments, Micro-g LaCoste Inc. (USA). The

‘‘g’’ software provides an estimate of the measure-

ment uncertainty, largely based on the instrumental

contribution to standard uncertainty at 1.1 lGal by

Niebauer et al. (1995). Gal (102m/s2) is accepted by

the Bureau International des Poids et Mesures as a

non-SI unit for use with SI to express acceleration

due to gravity (BIPM, 2025).

The uncertainty budget obtained from ‘‘g’’ does

not cover all instrumental components, and also site-

dependent uncertainties are not included. The most

complete uncertainty estimates for absolute gravity

measurements, combining the standard deviation of

the measurements with a full set of instrument-related

uncertainties and site-dependent uncertainties, are

typically those submitted by the gravimeter operators

to the international comparisons of absolute gravime-

ters. Starting with the International Comparison of

Absolute Gravimeters 2005, detailed uncertainty

calculations have been obligatory part of reporting

to the comparisons. The uncertainty estimation we

use in Sect. 3.2 is based on such submissions for the

FGI instruments. The JILAg measurements published

by Ma

¨kinen et al. (2007) were processed according to

the International Absolute Gravity Basestation Net-

work (IAGBN) Processing Standards (Boedecker,

1988), the predecessor of the International Terrestrial

Gravity Reference System (ITGRS) conventions

(Wziontek et al., 2021) and consistent with them.

Measurements from 2004 onwards were recently

reprocessed using the latest version of the ‘‘g‘‘

software, ‘‘g9’’ and following ITGRS conventions.

2.3. Relative Gravity Measurements

For the determination of the vertical gradient of

gravity at Aboa AG point, we have measured gravity

differences between different heights above the

gravity marker during several gravity campaigns at

Aboa using two types of relative gravimeters:

LaCoste-Romberg G and Scintrex CG-5. In absolute

gravimetry, the knowledge of the vertical gradient of

gravity above the measurement pier is required for

two purposes. First, the gradient over the drop range

of the gravimeter is needed in the rigorous equation

of motion. This can be mitigated via calculating the

absolute gravity values at the effective height of the

measurement (Pa

´linka

´s

ˇet al., 2012; Timmen, 2003),

where the measured gravity value is invariant with

respect to the gradient value. The effective height is

nominally 84 cm above the mounting surface for

JILAg, 121 cm above for FG5 and 127 cm

above for FG5X).

Additionally, the knowledge of the dependence of

gravity on height above the pier is required for

transferring the measured gravity values to any other

height, such as a common height for constructing

gravity time series measured with different types of

instruments. We transferred the measured gravity

values to the height 120 cm, close to the effective

heights of FG5.

2.4. Satellite Gravimetry

The satellite missions GRACE (Gravity Recovery

and Climate Experiment) and GRACE-FO (GRACE

Follow-on) provide to date the most sensitive space-

based method to observe mass redistribution of the

Earth (e.g. Landerer et al., 2020; Tapley et al., 2004).

The spatial resolution of GRACE is 200 km at

best. In this study we use GRACE regional mass

balance time series in interpretation of the gravity

trend observed at Aboa.

J. Na

¨ra

¨nen et al. Pure Appl. Geophys.

In particular, we use the Gravimetric Mass

Balance (GMB) product by a project lead by TU

Dresden under the European Space Agency’s (ESA)

Climate Change Initiative (CCI) (Do

¨hne et al. 2023;

Groh and Horwath, 2021). The TU Dresden GMB

products (https://data1.geo.tu-dresden.de/ais_gmb/)

are based on the monthly GRACE spherical-har-

monic solutions CSR RL06.2 by the Center for Space

Research at the University of Texas at Austin. They

use tailored sensitivity kernels referred to different

drainage basins. A gridded version has cells 50 

50 km and the unit of measure is millimetres of

equivalent water height (mm w.eq., or kg/m2).

2.5. Satellite Altimetry

Satellite altimetry is a commonly used method to

study the mass balance of ice sheets (e.g., Shepherd

et al., 2018). In order to study the mass balance

change around Aboa over the past 30 years with

altimetry, Surface Elevation Change (SEC) products

that combine data from several satellite missions are

needed. For our analysis we utilize two such data

products with monthly solutions openly available,

those of Nilsson et al. (2022) and Schro

¨der et al.

(2019b) (data available at the PANGAEA service

(Schro

¨der et al., 2019a). Nilsson et al. (2022)

combine data from Geosat, ERS 1 & 2, Envisat,

ICESat 1 & 2 and Cryosat-2 satellites and provide a

dataset with the timespan of 1985-2020 and 1:92 

1:92 km spatial resolution. Schro

¨der et al. (2019b)

combine data from Seasat, Geosat, ERS 1 & 2,

Envisat, ICESat and CryoSat-2 and provide a dataset

with the timespan of 1978-2017 and spatial resolution

of 10 10 km. The actual spatial and temporal

resolution, especially for the older altimetry missions,

is less than that of the data products. In this study we

chose to average the SEC values around Aboa over

an area with radius of 75 km providing a relatively

smooth time series with few artiﬁcial peaks due to

lack of data while not extending the area beyond the

outer edge of the Riiser-Larsen ice shelf, i.e., to sea

ice.

2.6. GPS Measurements at Aboa

FGI has operated a continuous GPS station,

named ABOA, at Aboa since 2003 with the motiva-

tion of, e.g., providing geometrical uplift rates due to

GIA. The station was GPS-only until January 2024,

when it was upgraded with a GNSS (Global Navi-

gation Satellite System) receiver and antenna. In

Andrei et al. (2018) we provide a description of the

station and an in-depth analysis of the GPS time

series using Precise Point Positioning (PPP) method.

In our analysis of the Aboa gravity time series we

primarily utilized the results from this article.

Since the Antarctic ﬁeld season 2011/12, we have

measured during six ﬁeld seasons the snow surface

heights along the slope of nunatak Basen down to the

surrounding ice sheet. The continuous GPS station at

Aboa was used as a base station for Real Time

Kinematic (RTK) GPS measurements. The motiva-

tion for these measurements has been to better

understand the changes in the local gravity environ-

ment with resolution not available through satellite-

based measurements. The thickness of the snow

cover in the vicinity of the absolute gravity observa-

tory is not very large, a few meters at most. However,

because of the proximity to the measurement point

and because the shape and spatial distribution of the

snow cover is constantly changing due to, e.g., wind

carving, it is beneﬁcial to understand the effect on

local gravity caused by these changes. The measure-

ments have been performed in the so-called stake-out

mode on 17 points arranged in a line leading from the

gravity point to a distance of 5 km (longest line in

Fig. 3). In stake-out we navigate to the same position

and measure the height difference relative to the

height measured in the ﬁrst campaign. The accuracy

of RTK-GPS measurements at Aboa is 3–5 cm,

however due to the natural undulation of the snow

surface (e.g., sastrugi formations) we estimate an

additional uncertainty of 0.3 m when comparing the

measured heights.

While repeated measurements of a single line

proﬁle provide an indication of mass change near the

gravity station, they cannot provide comprehensive

three-dimensional knowledge of the changes. To

provide three-dimensional volume (mass) change

information we have since the 2003/4 ﬁeld season

Three Decades of Repeated Absolute Gravity

mapped the elevations of the snow on the slope of

Basen up to 2 km from the gravity station either with

RTK-GPS measurements or laser scanning during

AG measurement campaigns. The RTK-GPS mea-

surements were made in fan-shaped line

measurements, illustrated in Fig. 3, where also the

5 km line proﬁle leading to the ice sheet is shown.

The line measurements are complemented with a

gridded measurement within the closest 100 ms of

the gravity point. Backpack-mounted laser scanner

was used in 2017 to measure the area previously

covered with RTK-GPS measurements with higher

spatial resolution and in 2020 a drone-based laser

scanner was used to extend the area further. Addi-

tionally, we have performed snow density

measurements that are needed to translate the eleva-

tion (volume) changes into mass changes. The

interpretation of the areal measurements is, however,

beyond the scope of this article due the difﬁculty in

realistically modelling the complex terrain surround-

ing the gravity laboratory and the especially the

largely varying density of snow. It is also to be noted

that before the advent of drone-based laser scanning

taking comprehensive measurements of the snow

ﬁelds around the gravity station, especially to the

south-west and north-east of the station, were not

possible due to existence of ice crevices, steep slopes,

and other areas not safely accessible on foot or on

snow mobiles.

Figure 3

Line proﬁles measured with RTK-GPS. The longest line is the 5 km proﬁle used in this article as a proxy for snow height changes near the

gravity point. The fan-shaped lines are measured with RTK-GPS attached to a snow mobile. Snowy areas not covered with the measurement

lines could not be reached safely due to, e.g., ice crevices. Background image is from Landsat Image Mosaic of Antarctica (LIMA, https://

lima.usgs.gov/)

J. Na

¨ra

¨nen et al. Pure Appl. Geophys.

2.7. Modelling the Newtonian Attraction of Ice Sheet

Mass Change

In addition to using terrestrial and satellite-based

data to study and understand the snow and ice mass

balance around Aboa, it is important to evaluate via

modelling how changes in the snow and ice mass

balance in the area surrounding the gravity station

would affect the absolute gravity trend.

A layer of ice or snow can be, as a ﬁrst

approximation, modelled as a circular cylinder with

deﬁned thickness and density, and inﬁnite radius. The

attraction of such a layer can be calculated with the

well-known analytical formula (e.g., Hofmann-Wel-

lenhof & Moritz, 2006)dgB¼2pGqh, where dgBis

the gravitation effect of a Bouguer plate (also known

as slab), Gis the gravitational constant and his the

thickness of the plate. However, while a Bouguer

plate provides an order of magnitude estimate for the

gravity effect, it is an over-simplistic approximation

for the changing mass balance around Aboa. The

absolute gravity point at Aboa is located on the slope

of a nunatak (Figs. 2and 10) where large areas are

snow free and no linear trend of overall snow mass

change has been observed. In addition, the grounding

line of the shelf ice is less than 20 km away at the

closest point, the elevation of the ice sheet is not even

and the elevation increases towards the south-east

(Fig. 2). To accommodate the topography of the area

surrounding the gravity point, a model is needed

where the nunatak is omitted from the area experi-

encing mass change. A further reﬁnement of the

model would be to include the sloping of the ice

sheet. The Bouguer plate has an analytical solution,

that can’t be easily reﬁned to, e.g., omit areas.

For removing the area of the nunatak and

including simple topography in the assessment of

the gravity effect of changing mass balance around

the gravity point at Aboa, the numerical method

developed by Nagy (1966) can be used. In this so-

called prism method the three-dimensional mass

affecting measured gravity is simulated by a model

consisting of mass elements in the shape of right

rectangular prism. The vertical component of the

gravitational attraction of each prism, as measured by

a gravimeter from a known horizontal distance and

elevation to the prism, is calculated and the sum of

these components provide the cumulative gravity

effect of the mass elements. Using the prism method,

we developed a Python program to calculate the

cumulative gravity effect of increasing snow/ice mass

as measured by an AG at Aboa. In the program, the

added mass on top of the ice sheet surrounding Aboa

is considered as a cylindrical slab of even thickness

consisting of volume elements or prisms with

adjustable dimensions and density. The height of

the measurement point above the slab can be also

adjusted. The nunatak is considered as a hole in the

middle of the slab with adjustable radius, i.e. there

are no prisms within the area of the nunatak. We kept

the dimensions of the prisms homogeneous within

each calculation emulating homogeneous mass

change over the area.

We further reﬁned the program to accommodate

for the fact that the location of the gravity observa-

tory is not on the top of the nunatak, but rather on the

side, by creating a central mask consisting of

semicircles with different radii. The ice sheet is

approximately 2 km closer to the laboratory in the

South than it is in the North (Fig. 3). The simulated

ice slab is also tilted by 0.38, an average value

derived from Bedmap2 elevation model, to approx-

imate the sloping of the ice sheet towards the

grounding line of the ice shelf. The prism method

would allow to model, e.g., complex topographies,

non-homogeneous snow accumulation, and density

variations within the accumulated snow. However,

such modelling is beyond the scope of the current

paper.

3. Results

In this section, we present the absolute gravity

time series at Aboa. To understand the trend in the

AG time series, we present satellite-based observa-

tions with implication on the regional mass balance

around Aboa, crustal motion at Aboa as measured

with GPS, RTK-GPS based elevation change mea-

surements near the Aboa gravity observatory and

results from our prism gravity simulation program

which simulates the cumulative gravity effect from

changes in the mass of the ice sheet surrounding

Aboa.

Three Decades of Repeated Absolute Gravity

3.1. Vertical Gradient of Gravity

We present the results of vertical gradient of

gravity measurements in Table 1. Each value is an

average of several measurements at the indicated

height, usually measured in six ladder sequences. The

observations are corrected for tides and for minor

(one-mm-level) variation in heights between the

different sequences. The ﬁnal gravity values are then

obtained in a network adjustment together with the

removal of drift. The network adjustment also

provides standard deviation statistics to assess the

quality of the measurements.

The gradient is not constant (Table 1). This is

mostly due to the massive concrete pier of the gravity

station (Ma

¨kinen, 2010). While massive piers are

rather common at absolute stations in general, at

Aboa a high pier was needed in order to raise the

ﬂoor of the laboratory well above ground. This has

prevented wind accumulation of snow around the

building.

Fitting a polynomial in height to the measured

gravity differences we obtain gðzÞgð0Þ¼437:4

2:8lGal=mzþ15:22:0lGal=m2z2, where g

is the gravity value in lGals and zis the height above

gravity marker. Figure 4depicts the obtained gradient

function and the relative gravity measurements.

3.2. Absolute Gravity Time Series at Aboa

As discussed in Sect. 2.2 the 30-year long

absolute gravity time series at Aboa has been

measured with three different instruments with

differing measurement uncertainties and measure-

ment heights. Following Bilker-Koivula et al. (2021)

we assign to the JILAg-5 measurements the uncer-

tainty of 10 lGals to the FG5-221 results an

uncertainty of 2.6 lGal and to the FG5X-221 results

2.3 lGal. These values do not take into account

environmental gravity changes such as changes in the

nearby snow and ice masses and their spatial

distribution.

We also apply a constant offset of 7lGal to the

JILAg-5 measurements relative to FG5(x) measure-

ments as determined by Bilker-Koivula et al. (2021).

Ocean tidal loading is corrected using the FES2004

model (Lyard et al., 2006) which is the most modern

model embedded in ‘‘g9’’ software. Global ocean tide

models in general are not optimal for Antarctica due

to several factors, including sparse availability of data

for modelling. However here we assume, that mea-

suring continuously for several days or even weeks

and averaging the results reduces the residual errors

in ocean tide corrections to sub-lGal level and the

residual error is included in our overall error budget.

The correction for the self-attraction of the gravime-

ter is 1.48 lGal for the FG5-221 and 1.17 lGal

for the FG5X-221 (Niebauer et al., 2013). The

correction for the laser beam diffraction in the

interferometer is ?1.37 lGal, based on Van Wes-

trum and Niebauer (2003) and measured beam

properties. The gravity values were calculated at the

effective height of measurement where the gravity

value is invariant of the gradient value used (Tim-

men, 2003). The frequency of the rubidium oscillator

of the gravimeter was interpolated from calibration

Table 1

Relative gravity measurements of the vertical gradient of gravity at Aboa

Height 1 (mm) Height 2 (mm) Height 3 (mm) g(H2–H1) (lGal) g(H3–H1) (lGal) Date Gravimeter

67 806 1329 312.9 527.0 7.2.2004 LCR G

67 806 1329 311.5 524.0 8.2.2004 LCR G

129 1299 485.9 1.2.2012 CG-5

128 741 1307 263.0 491.1 2.2.2017 CG-5

128 706 1300 245.9 486.7 25.1.2020 CG-5

Heights are determined from the gravity station marker. Middle height measurement from 2012 was omitted from analysis due to an

abnormally high ﬁtting residual in network adjustment which is most likely due to an unrecoverable erroneous height determination at the

time of measurement. Earlier measurements with LaCoste Romberg G gravimeter were also omitted since they were taken at only two heights

and with visual readout of data causing large uncertainties. Each gravity value represents an average of several measurements at the indicated

height

J. Na

¨ra

¨nen et al. Pure Appl. Geophys.

measurements before and after the Antarctic cam-

paign in the case of 2005 and 2012 measurements, for

2017, 2020, and 2024 measurements the frequency of

the rubidium oscillator was controlled by 1 PPS

signal from GPS and veriﬁed with in situ compar-

isons with a GPS-controlled quartz oscillator. More

detailed discussion about corrections applied to

absolute gravity measurements during postprocessing

is beyond the scope of this paper, such discussion can

be found in, e.g., Ma

¨kinen et al. (2007).

For purpose of constructing a time series, all the

measurements were transferred from effective height

to a common height of 1.2 m, which is close to the

effective height of FG5 measurements. The transfer

was done using 400.6 lGal/m as the value of the

vertical gravity gradient, derived from repeated

relative gravity measurements (Sect. 3.1). The abso-

lute gravity values at Aboa Station are presented in

Table 2and in Fig. 5.

Comparing the results from 1994 and 2024 we

note that the gravity at Aboa has increased 48:2

10:3lGals in 30 years (uncertainty calculated with

root of sum squares method), yielding an average

change of 1.6 lGal/year. Figure 5shows a near-linear

gravity increase of 40 lGal in the 18 years of the 5

latest measurements. There seems to be an inﬂection

point or change in the trend around 2005.

Absolute gravity time series are traditionally ﬁtted

with linear functions (e.g., Bilker-Koivula et al.,

2021). The underlying rationale is then that the

signal of interest (like the GIA) is inherently linear

over the time span of the AG measurements and

environmental effects are considered noise that

Figure 4

Least-squares ﬁt of a 2nd order polynomial to the relative gravity

measurements. A constant gradient of 419.2 lGal (average

gradient between heights of 0.2 and 1 ms) has been subtracted to

demonstrate the nonconstant nature of the gradient. Shading

indicates the standard error of the ﬁtted polynomial function

relative to the height of 1.2 ms. Measurements with the LaCoste

Romberg G gravimeter in red color and measurements with the

Scintrex CG5 gravimeter in blue

Table 2

Absolute gravity values at Aboa, transferred to a common height of 1.2 ms

Gravimeter Mean date Number of sets g (lGal) Uncertainty 1r(lGal)

JILAg-5 18.1.1994 1002 982622559.2 10.0

JILAg-5 20.1.2001 852 982622568.0 10.0

FG5-221 6.2.2004 99 982622565.9 2.6

FG5-221 8.12.2005 286 982622567.8 2.6

FG5-221 30.1.2012 308 982622582.4 2.6

FG5X-221 24.1.2017 636 982622591.4 2.3

FG5X-221 20.1.2020 157 982622592.6 2.3

FG5X-221 30.1.2024 610 982622607.4 2.3

Here a constant offset correction of 7lGal is applied to the JILAg-5 as determined by Bilker-Koivula et al. (2021)

Three Decades of Repeated Absolute Gravity

averages to zero over time. From the magnitude of

the gravity change seen in Fig. 5and from compar-

ison with vertical motion (see later) it is obvious that

GIA cannot be the dominant factor here. Neverthe-

less, we ﬁtted a linear function gðtÞ¼atþb

(where g(t) is the absolute gravity value, ais the

gravity trend, and bis a constant) to the Aboa

absolute gravity time series with least-squares

method using the inverse squared measurement

uncertainties (Table 2) as weights. However, as can

be seen in Fig. 5, the linear function does not give a

good ﬁt to the earliest measurements. We then ﬁtted a

2nd order polynomial function gðtÞ¼at2þb

tcto the data via least-squares method. The best ﬁt

coefﬁcients were a¼0:02845, b¼0:8305, and

c¼26:95. As can be seen in Figs. 5and 6, the 2nd

order polynomial ﬁts almost all measurement points

within their error margins. We refer to the residual

plot (Fig. 6) to provide a goodness-of-ﬁt comparison

between the linear and 2nd order polynomial func-

tions. The overall slightly lower residuals of the 2nd

order polynomial, especially to the earliest measure-

ments albeit with most uncertainty, indicate that the

gravity change at Aboa during the past three decades

is nonlinear.

Martı

´n-Espan

˜ol et al. (2016) provide a review of 8

widely used GIA models for Antarctica, with predic-

tions of GIA vertical velocities at Aboa . All models

predict uplift, which would translate into gravity

decrease. We calculate the gravity change rates using

the result ð_

hÞ¼0:154 by Wahr et al. (1995),

where _

gis the gravity change rate and

hthe

geometrical vertical velocity. The number they quote

is ?0.154 lGal/mm after the free-air correction to

gravity for the vertical motion, which translates to 

0.308 ?0.154 = 0.154 lGal/mm without the

correction. They found this within-model relationship

numerically, applying different deglaciation histories

and Maxwellian rheologies. Theoretical motivation

for such a linear relationship (with the factor

depending on the particular deglaciation) was later

provided by Olsson et al. (2015), and an empirical

veriﬁcation in Fennoscandia by Olsson et al. (2019).

In Table 3we have calculated the gravity change

rates for Aboa from the vertical rates of the 8 GIA

models reviewed by Martı

´n-Espan

˜ol et al. (2016,

Supplementary information).

Figure 5

Absolute gravity at Aboa ﬁtted with linear and polynomial functions

J. Na

¨ra

¨nen et al. Pure Appl. Geophys.

In order to interpret the large observed gravity

increase, which is in contradiction to gravity decrease

expected from GIA models, we need to utilise results

from several independent satellite-based and terres-

trial geodetic measurement methods as well as

modelling to study the environment and ground

motion at and around Aboa.

3.3. Satellite-Geodetic Measurements of the Western

Dronning Maud Land

In the previous section we concluded that the

large gravity increase at Aboa cannot come from GIA

and consequently must be due to contemporary

changes in snow and ice sheet mass at the local and

regional level. The Dresden GMB data (Groh and

Horwath, 2021) includes a gridded product of

monthly regional mass change since 2002–04, with

grid size 50 50 km2, in millimetres of equivalent

water height. The interpretation is slightly compli-

cated by the fact that the GIA correction applied to

the data is published only at the basin level (Groh and

Horwath, 2021, Supplementary information). For the

the basin AIS04 (https://earth.gsfc.nasa.gov/cryo/

data/polar-altimetry/antarctic-and-greenland-

drainage-system) in which Aboa is located the cor-

rection of 0.9 Gt/a with a standard uncertainty of 2.2

Gt/a. Given the area of the basin ( 264,000 km2)

this means an average water equivalent of 3:5mm/

a with an uncertainty of 9 mm/a.

In Fig. 7we present the time series from the

Dresden GMB product in a region around Aboa. We

selected and averaged from the GMB spatially

gridded dataset those points that are within a

100 km radius from Aboa. The resolution of the

dataset would allow for more tight spatial boundaries.

However considering that the actual spatial resolution

of GRACE is more than 200 km, the radius of

100 km was considered prudent. The selection

yielded 9 grid points with data covering an area of

Figure 6

Residuals of linear and polynomial ﬁts to the measured gravity values. Error bars indicate 1rerror in the measurements

Table 3

Vertical velocities and gravity change rates predicted by GIA-

models at Aboa

Model Land uplift (mm/a) Gravity change (lGal/a)

W12 1.32 0.21

IJ05_R2 0.24 0.04

ICE-6G_C(VM5a) 3.24 0.50

A13 0.65 0.10

AGE1b 0.19 0.03

R09 1.93 0.30

G14 1.79 0.28

RATES 1.89 0.29

Three Decades of Repeated Absolute Gravity

22,500 km2. Four grid points within the search area

were masked out in the GMB dataset as being ocean

due to Aboa’s proximity to the ice sheet grounding

line. The trend in averaged surface mass from 2004

onwards is about 50 mm/a. This is a magnitude larger

than the GIA correction in the GMB product or its

uncertainty (see above), such that the conclusion of a

large increase in surface mass does not seem to

depend on the GIA model. The model used by Groh

and Horwath (2021) is the IJ05_R2 that predicts a

vertical velocity of ?0.24 mm/a at Aboa. But even

the largest GIA-predicted vertical velocity in Table 3

is ?3.24 mm/a from the ICE_6G_C(VM5A). An

order-of-magnitude calculation with upper mantle

density 3500 kg/m3would still give a mass increase

of 10 mm/a in water equivalent. The Aboa AG time

series is also shown in Fig. 7. The trends GRACE and

AG time series correlate qualitatively well providing

a link between the regional mass increase observed

with GRACE and the gravity increase observed at

Aboa.

In Fig. 8we illustrate the averaged surface

elevation change from the two altimetry datasets

around Aboa. These data indicate an increase of up to

1.5 ms of elevation since the beginning of the AG

measurements. The increase is most notable since

2005 which correlates with an inﬂection point in AG

data at around 2004. The trend is similar to that in the

GRACE GMB time series indicating that the mass

increase observed with GRACE is due to increased

amount of snow and ice. The differences in the details

of the two curves, e.g. the ﬂattening in the altimetry

since 2013 could be due to the different averaging

radiuses. Also, the surface elevations from altimetry

should be converted to mass taking into account ﬁrn

consolidation.

3.4. Elastic Deformation and Vertical Velocities

Measured with GPS

The large increase in regional mass observed with

GRACE and indicated via surface elevation increase

measured by altimetry (Figs. 7and 8) should lead to

elastic deformation and a negative contribution to the

vertical velocity budget at Aboa. Thomas et al.

(2011) estimated a regional elastic component of 

0.22 mm/a. This value is proportional to the mass

increase rate, which according to GRACE measure-

ments has remained constant or even increased

slightly since 2011. Therefore the value can be

considered as a valid approximation of present day

elastic velocity.

In Andrei et al. (2018) we estimated, based on

PPP solutions from two different analysis software, a

Figure 7

Mass change (in units of mm water equivalent) averaged over the area with the radius of 100 km around Aboa obtained from the GRACE

GMB dataset (Groh and Horwath, 2021) plotted together with the absolute gravity measured at Aboa (in lGal). Scaling of the two types of

measurements is arbitrary with the aim of illustrating the qualitative correlation between the AG and the mass change estimated from the

GRACE(FO) time series. As a Bouguer layer, 1000 mm of water corresponds to 42 lGal (Fig. 11)

J. Na

¨ra

¨nen et al. Pure Appl. Geophys.

linear land uplift rate 0:75 0:35 mm/a for Aboa,

which we contributed to Glacial Isostatic Adjustment.

The GPS data and trend ﬁtting are shown in Fig. 9.

Subsequently, we compared the measured uplift rate

to the predictions from eight GIA models. In this

comparison we did not consider the elastic vertical

velocity component due to contemporary mass bal-

ance. The impact of using the value from Thomas

et al. (2011) would have been to increase the uplift

rate to 0.97 mm/a for the comparison with GIA

models that do not take elastic deformation into

account. Only one model prediction, that of A13 GIA

model (A, 2013), was within the error margin of the

measured uplift rate. Notably the prediction from the

IJ05_R2 model, 0.24 mm/a, used to remove GIA

effects in the Dresden GMB product is beyond the

error margin of our measured uplift rate. Uplift for

ABOA has been found in other GNSS analysis as

well, e.g., in a recent paper by Buchta et al. (2025b).

Their reprocessing of all available GPS data from

Antarctica (data openly available at Buchta et al.

(2025a) yielded an estimated uplift of 0:10 0:19

mm/a for ABOA. The apparent discrepancy between

the uplift rate in Andrei et al. (2018) and Buchta et al.

(2025b) can be at least partially explained by their

use of different reference frames (e.g., Konyk et al.,

2025; Liu et al., 2021). ITRF2008 was used in Andrei

et al. (2018) and IGb 14, which is a realization of

ITRF2014, in Buchta et al. (2025b).

Further analysis of the GNSS uplift rates is

beyond the scope of this article. For analysing the

gravity change it is sufﬁcient to note that the area

around Aboa is currently experiencing a land uplift as

also predicted by GIA models.

3.5. Snow Height Change from RTK-GPS

As described in Sect. 2.6, we have since 2011/12

ﬁeld season measured a line proﬁle of height changes

on the slope of Basen Nunatak from the gravity

observatory to a distance of 5 km in the surrounding

ice sheet. These measurements have been performed

with the RTK-GPS technique. The results of the

RTK-GPS measurements are depicted in Fig. 10.

While a line measurement obviously can’t provide a

comprehensive picture of the overall three-dimen-

sional changes in the snow and ice mass distribution

it nevertheless gives an indication of the scope of the

changes. The measurements show an up to 3 m

increase in snow height during the last 12 years with

signiﬁcant variation season-to-season. Most

notable increase within the measured line occurred

between the two last measurement epochs.

Figure 8

Average ice sheet surface elevation change at a radius of 75 km around the gravity laboratory at Aboa analyzed from multi-mission satellite

altimetry datasets (Nilsson et al., 2022; Schro

¨der et al., 2019b). The absolute gravity measurement epochs are indicated with dotted lines

Three Decades of Repeated Absolute Gravity

Figure 9

Precise point positioning solution to the ABOA GPS data as published in Andrei et al. (2018)

Figure 10

RTK-GPS measurements of the surface height change in a straight line from the gravity lab at Aboa to a distance of 5 km on the surrounding

ice sheet. The results are shown on the top plot as changes relative to the slope proﬁle measured during the 2011/2012 ﬁeld measurement

season (bottom plot)

J. Na

¨ra

¨nen et al. Pure Appl. Geophys.

3.6. Modelled Gravity Effect Due to Increased Ice

Sheet Mass

The terrestrial and space-geodetic measurements

of the ice sheet behaviour around Aboa indicate a

mass increase during the time scale of the AG time

series. Therefore, it is of interest to explore whether a

mass increase of the ice sheet around Aboa could

explain the observed gravity increase. In Fig. 11 we

demonstrate the Bouguer slab (Sect. 2.7) gravity

effect as a function of slab thickness and density. It

can be noted that a 3 m thick slab of snow or a 1.3 m

thick slab of ice would produce the 48 lGal

change observed in the absolute gravity time series.

This provides an indication that the observed gravity

increase is indeed due to the mass increase in the

surrounding area. However, as pointed out in Sect.

2.7, Bouguer slab is an over simplistic approximation

for the snow and ice surrounding Aboa.

To provide more realistic assessment of the

gravity effect of added ice mass in the ice sheet

surrounding Aboa, we next used the prism gravity

program (Sect. 2.7) to calculate gravity effects from

slabs of ice with central holes, simulating the nunatak

Basen. In Fig. 12 with symmetrical central mask and

no tilting of the ice sheet, we explore how the

cumulative gravity effect changes while varying ice

slab parameters as well as the measurement height

above the slab. For this exercise we chose to use the

density of ice, 910 kg/m3as eventually accumulated

snow transforms into ice on the ice sheet (Granberg

et al., 2009). From the RTK-GPS proﬁle (Fig. 10)we

selected 120 m as the reference elevation above the

ice sheet and 1000 m as the distance from the gravity

observatory to the ice sheet. We use 8 ms as a

maximum feasible change of the close-by ice sheet

elevation over 30 years.

As can be seen in Fig. 12, after removing mass

change from the closest 1000–2000 ms, the model

can’t reproduce the 48 lGal cumulative gravity

effect with any reasonable set of ice slab parameters.

Using the density of snow would reduce the gravity

effect further.

We further reﬁned the modelling. In Fig. 13 we

mask the nunatak with two semicircles of a deﬁned

radius, 1 and 2.5 km to better simulate the actual

shape of the nunatak around the gravity station. We

also introduced a tilt of 0.38to the ice sheet,

obtained from the BEDMAP 2 elevation contours

(Fig. 2) perpendicular to the dividing line between the

mask halves to simulate the slope of the ice sheet.

The effect is to further reduce the cumulative gravity

effect from the mass change in the ice sheet. With

8 ms of accumulated ice we reproduce approximately

half of the gravity change observed over 30 years.

Figure 11

Gravity effect from Bouguer slabs of different thicknesses and densities. Horizontal line depicts the 48 lGal gravity change observed at

Aboa over the past 30 years. Vertical lines indicate the typical thickness of snow and ice around Aboa, 395 and 910 kg/m3respectively

Three Decades of Repeated Absolute Gravity

4. Discussion

Absolute gravity measurements made in Antarc-

tica are often reported only in technical papers or

conference presentations. Reviewed scientiﬁc articles

on the topic are scarce, especially those covering

measurements from Dronning Maud Land. The only

compilation of AG measurements in Antarctica is

¨kinen et al. (2007) reporting 23 measurements

from 12 gravity stations that had been measured up to

2004. They provide time series for two stations in

DML. For Aboa they report gravity trend of 0:5

0:5lGal=a and for Syowa Station

0:30:4lGal=a. Kazama et al. (2013) report

additional measurements at Syowa with A10

gravimeter with the latest measurements in 2012.

Their analysis of the Syowa gravity series which

starts in 1994, provides a gravity trend of

0:09 lGal=a. It is to be noted that Syowa is located

1900 km to the East from Aboa and on an area with

much different topography to that of the surroundings

of Aboa. None of the reported gravity change values

in literature for DML are close to the 1:6lGal=a

(1:9lGal=a after the 2004) we have obtained for

Aboa.

As shown in Sect. 3.2 the gravity at Aboa station

has increased by 48:210:3lGals in the past 30

years. This increase is in apparent contradiction with

the land uplift measured at the Aboa GPS station

(Sect. 3.4) and GIA model predictions (Sect. 3.2)

which indicate gravity decrease instead. Following on

the discussion on the GIA-induced gravity change

and considering the land uplift rate, the expected

gravity change at Aboa would be 0:12 0:05 lGal=a

resulting in a total gravity decrease of 3:61:5lGal

in 30 years. Large regional mass increase has been

Figure 12

Cumulative gravity effect of a slab of ice as measured with a gravimeter (effect in the direction of the gravity gradient). aThe cumulative

effect without a hole simulating the nunatak. Extended to inﬁnite distance this would be the effect of a Bouguer slab. bThe effect of changing

the size of the central hole in the slab. cThe effect of varying the thickness of the ice slab. dThe effect of changing the elevation of the

gravimeter above the slab

J. Na

¨ra

¨nen et al. Pure Appl. Geophys.

observed with GRACE (Sect. 3.3) since 2005. The

GRACE GMB time series qualitatively correlates

with the AG time series indicating that the large

gravity increase at Aboa is linked to the regional

mass increase. Mass change in the area surrounding

Aboa affects the measured gravity via direct attrac-

tion and has the potential to cause elastic deformation

of the ground. In Sects. 3.3 and 3.5 we have

demonstrated that the surface elevation around Aboa

and to a distance of several tens of kilometres has

increased over the time of the absolute gravity mea-

surements, providing an explanation for the mass

increase via additional snow and ice in the region. It

is worth noting that the altimetry data shows an

inﬂection point in surface elevation trend around

2005 which is supported by our gravity time series.

Increased precipitation over the Dronning Maud

Land region during the past 20 years has been

reported by several authors providing an explanation

to the positive mass balance. Velicogna et al. (2014)

report a snowfall event, unique in GRACE record,

over DML in 2009 Similar episodes of high snowfall

have been detected in the past as well (Lenaerts et al.,

2013; Van Wessem et al., 2014). Since 2009, ele-

vated snowfall rate has persisted in DML, which may

be indicative of a new trend in surface mass balance

over the coast of Antarctica facing the Atlantic

Ocean. Recent results suggest that snowfall in this

sector has been 25% higher than during the pre-in-

dustrial period (Medley & Thomas, 2019). Similarly,

surface mass balance peaked in the Antarctic Penin-

sula in 2016, but the increase did not persist after

2016. Another GRACE-based analysis by Velicogna

et al. (2020) report a cumulative mass increase of

980Gt between 2009 and 2020 in DML. However,

Aboa lies just outside the area they included in their

analysis. The positive mass balance is observed via

other methods as well. Rignot et al. (2019) report a

mass increase of 25Gt on the drainage basin of the

Riiser-Larsen ice shelf for period 1979–2017 using

the input–output method. Nilsson et al. (2022) report,

based on the analysis of their combined SEC dataset,

that the DML region has started to show extensive

elevation gain due to signiﬁcant increases in snowfall

beginning around 2009.

In Sect. 3.6 we simulated the effect of the ice

mass increase in the region around Aboa to the

gravity point in order to evaluate how much of the

observed gravity trend could be explained. Our most

detailed simulation could only reproduce about half

of the gravity increase, when using the density of ice

in the calculation. This discrepancy between

observed and simulated gravity change becomes even

larger if we consider that the GPS-measured land

Figure 13

Cumulative gravity effects of tilted slabs of ice of varying thickness. The tilt of the slabs is 0.38. The gravimeter is assumed to be 120 ms

above the center of the slab and the center of the slab is masked with two semi-circles, one 2.5 km in radius and the other 1.0 km

Three Decades of Repeated Absolute Gravity

uplift indicates that a small GIA-induced gravity

decrease is also taking place. A likely explanation for

this discrepancy is that the topography of the nunatak

Basen and that of the surrounding ice sheet are not

modelled with sufﬁcient detail. Additionally, and

potentially more crucially, the ice and snow mass

change within the closest 1000 ms to the gravity

observatory is not included in our simulations.

Our RTK-GPS-based snow height measurements

along a 5-km line leading from the gravity point to

the surrounding ice sheet (Fig. 10) show that there

has been signiﬁcant annual mass variation and also a

positive trend since 2012. The trend is apparent not

just on the ice sheet, but also on the slope of the

nunatak. The contribution of a mass element to the

gravity measurement at a given point is inversely

proportional to approximately the third power of the

distance. In other words, the effect of mass variations

from the closest 1000 ms could dominate the gravity

signal, as also shown in the top left plot of Fig. 12.

The closest 1000 ms to the gravity point are on the

slope of the nunatak and experience constant wind-

driven mass redistribution. Thus, a one-dimensional

measurement can’t be used to realistically model the

snow mass change on the whole slope. To create a

three-dimensional model the cumulative gravity

effect of mass variations from this area, high-reso-

lution and accurate digital elevation models (DEMs)

of the area at the time of the absolute gravity obser-

vations are needed. In addition, the calculations are

sensitive to the density of the snow and ice which is

not uniform spatially nor temporally on the slope of a

nunatak. As discussed in Sect. 2.6, we have during

several past AG campaigns done measurements to

allow three dimensional assessment. Preliminary

results from calculating the cumulative gravity effect

at the Aboa gravity point caused by mass changes

around the station indicate a season to season varia-

tion in the order of several lGals and large seasonal

variation in the mass distribution in the area. A full

analysis of the gravity effects due to local mass bal-

ance is challenging to make, for reasons stated in

Sect. 2.6, and is left as a topic for further research.

Although the mechanisms behind the gravity

trend observed at Aboa are not yet fully understood, it

is apparent from our simulations together with the

terrestrial and satellite geodetic measurements that

the increased precipitation in DML is currently the

dominating factor behind the trend.

5. Conclusions

The absolute gravity time series at Aboa were

started with the motivation of measuring the gravity

change due to GIA and furthermore advancing the

understanding of GIA mechanism in the area. How-

ever, it has become apparent that factors other than

GIA dominate the absolute gravity change at Aboa.

Added snow and ice mass due to increased precipi-

tation in the area introduces a gravity change via

direct attraction that is almost an order of magnitude

greater than the expected GIA signal. Regardless of

not currently being usable for the intended purpose,

the AG time series provides an independent ground

truth conﬁrmation for the mass increase observed in

the area with GRACE and indicated by satellite

altimetry. The trend in the three-decades-long AG

time series has an inﬂection point around 2004 which

provides provisional support for the reported increase

in precipitation in DML during the past 20 years.

Using AG for understanding the GIA is an estab-

lished method in areas that experienced Holocene

deglaciation, such as Fennoscandia and North

America. Environmental gravimetric signals due to,

e.g., hydrology may overshadow the GIA signal in

the short term in those areas (e.g., Bilker-Koivula

et al., 2021). This can be overcome with extended

time series and added data points as most such signals

are considered non-systematic and will cancel out in

the long term. However, our study highlights the need

to use caution when using AG to provide gravity rates

attributed solely to GIA in areas with ongoing ice and

snow mass balance changes, such as Antarctica and

Greenland. The ongoing changes in mass balance

may introduce secular gravity trends that can mask

the GIA signal.

Acknowledgements

The data used in this work has been collected with

support by the Finnish Antarctic Research Program

J. Na

¨ra

¨nen et al. Pure Appl. Geophys.

FINNARP during several Antarctic research

expeditions.

Author Contributions JM and JN contributed to the study

conception and design. Material preparation, data collection

and analysis were performed by JN, JM and AR-H. Funding

acquisition was carried out by JM, JN, and MN. The ﬁrst draft

of the manuscript was written by JN and all authors

commented on previous versions of the manuscript. All

authors read and approved the ﬁnal manuscript.

Funding

Open Access funding provided by National Land

Survey of Finland. This research was partially funded

by the Research Council of Finland (decision number

364868).

Data Availability

Data is provided within the manuscript.

Declarations

Conﬂict of interest The authors declare no competing

interests.

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Three Decades of Repeated Absolute Gravity

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