GOCE and Antarctica Rene Forsberg DTU Space, Denmark Credit: Planetary visions/CPOM/ESA CryoSat

Antarctica – why is GOCE useful? A poorly mapped continent – 13.8 million km 2, 6 x Greenland, 2 x Europe 98% ice covered, Ice up to 4.5km thick, E Antarctica stable, W and Peninsula loosing mass GOCE objective: gravity to map subglacial terrain and underlying geological features Pine Island gletscher Antarctic Peninsula West East Antarctica Antarctica last remaining void of gravity field data on the planet..GOCE give a coherent picture

Antarctica and GOCE (2) Antarctica gravity field has global implications – gravity pertubates satellite orbits: - Environment and polar monitoring satellites such as ESA CryoSat and the upcoming Copernicus constellation degraded without knowledge of accurate polar gravity Complete coverage of global gravity a century-old ”holy grail” of geodesy - determination of the ”geoid” requires knowledge of global gravity GOCE satellite detection of high-resolution gravity change due to melt of large glaciers GOCE has provided a first coherent detailed view of the Antarctic gravity field – High resolution and accuracy => Useful data for geophysics and glaciology The current global standard model of the gravity field: EGM2008 (US NGA): Red show areas:void of data, other colours show gravity data availability at varying quality levels

Antarctica gravity field from GOCE BEDMAP2 - H. Pritchard, British Antarctic Survey Latest GOCE gravity map (Release 5) of Antarctica – major structures can clearly be traced … a first Antarctic sub-ice terrain compiled from airborne radar measurements A B C D E A – Lake Vostok (largest sub-ice lake) B – Aurora Basin (thick sediment layers) C – Recovery ice stream valley and lake D – Trans-Antarctic Mountains E – Pine Island Glacier sub-ice valley G – Gamburtsev sub-ice mountain Unit: mGal ~ 1  g (millionth of g) G

BEDMAP2 seen from West – many regions need data H. Pritchard, BAS / NASA visualization

Existing gravity in Antarctica and GOCE SCAR Antarctic Geoid Project AntGP.. complement ADGRAV, BEDMAP Some recent data: ICEGRAV (blue), ICECAP (green), ICEBRIDGE (grey) Current AntGG project gravity coverage (M. Scheinert, TU Dresden) Expensive field operations in last decade … airborne gravity filling in major voids as part of integrated geophysics projects (US, Russia, Germany, UK, … gravity low priority usually)

NASA IceBridge Orion-P3 and DC8 (operating from S America / McMurdo) DTU Space/IAA/NGA ICEGRAV (Antarctic bases – Troll / Marambio)

Airborne gravity and GOCE – ICEGRAV (DTU-NPI-BAS cooperation) Error estimate: ~3 mGal from cross-over analysisDifference to GOCE: ~ 1 mGal bias, 22 mGal rms - Confirms good quality of airborne survey (and GOCE) - Halley (UK) Belgano(Arg) Troll (N) FD83 (Rus.)

Recovery Lakes 2013 survey: Ops from Halley, Belgrano and FD83 / Troll camp support

Gravity and sub-ice terrain – DML Gravity free-air (mGal) Bedrock elevation (blue: below sea level)

Using gravity for ice stream bed elevation (example of 2-D gravity inversion when ice radar fails). NorthSouth Radar gap U Texas/ D Young radar

Some ”surprising” GOCE results … heatflow link … ESA Dome-C SMOS/GOCE campaign Jan 2013 (AWI, Germany / DTU-Space) SMOS absolute temperature (T B, K) Gravity from GOCE and airborne data (mGal) Dome-C area size 500 x 500 km; Macelloni et al (in prep.) GOCE and airborne gravity correlates with T B radiometer data from the SMOS satellite.. due to correlation of gravity with ice thickness and heat flow insulation by overlaying ice? Dome-C

ESA Dome-C SMOS/GOCE campaign – validation of GOCE gradients (H. Yildiz, Tscherning, Forsberg) Dome-C airborne gravity (overlaid on GOCE) GOCE gradient field at satellite altitude (colour scale –80 to 80 mE except T yz ) Validation on 5 ”good” gradients ~ 0.02 E r.m.s. (ESA Dome-C report) [least-squares collocation upward continuation]

Some surprising GOCE results (2) … GOCE measures climate-related gravity changes; mass loss of individual glaciers in W Antarctica resolved for the first time Baumann et al, Geophysical Research Letters, 2014 GRACE trend (mm w.eq.) GOCE mass loss

GOCE Antarctica - the Polar Gap GOCE has left gap south of 83  S due to satellite orbit.. GOCE data not global Arctic gap covered (ArcGP) Southern gap no terrestrial data (only GRACE) Airborne gravity can deliver the missing data Difference in geoid from the two official R5 GOCE models Polar gap problem Arctic gravity field from airborne, surface and submarine data (ArcGP compilation)

Current planning: US NSF C-130 aircraft operating from McMurdo BAS-DTU team operating from remote camps Fuel provided at US South Pole Station Primary funding: ESA + NSF (tbc) FD83 field camp McMurdo Thiel Mts camp ESA-NSF International effort 2015/16 ”PoleGap” BAS / DTU Space / Columbia Univ. Lines coordinated with NASA-IceBridge => Truly global ”final” GOCE gravity field NSF ESA fuel cache (IceGrav-2013) NSF US south pole station

Conclusions - GOCE data in Antarctica has covered large ”white spot” regions - Useful data for geophysics, glaciology and climate change - South pole gap to be covered by airborne gravity 2015/16.. tbc