Year: 2025
Type: article
Abstract: The Greenland Ice Sheet’s contribution to global sea-level rise is accelerating1 due to increased melting of its bare-ice ablation zone2–6, but there is growing evidence that climate models overestimate runoff from this critical area of the ice sheet7–12. Current climate models assume all bare ice runoff escapes to the ocean, unlike snow covered areas where some fraction of runoff is retained and/or refrozen in porous firn13–15. Here we use in situ measurements and numerical modeling to reveal extensive retention and refreezing of liquid meltwater in bare glacial ice, explaining chronic runoff overestimation by climate models. From 2009–2018, refreezing of liquid meltwater in bare, porous glacial ice reduced meltwater runoff by 11–23 Gt a-1 in southwest Greenland alone, equivalent to 10–20% of annual meltwater production. This mass retention is commensurate with current estimates of climate model ice sheet meltwater runoff uncertainty, and may represent an overlooked buffer on projected runoff increases for the coming century16. Inclusion of bare-ice retention and refreezing processes in climate models therefore has immediate potential to improve forecasts of ice sheet runoff and its contribution to global sea-level rise.
Source: Nature Communications
Institutions: Pacific Northwest National Laboratory, University of California, Los Angeles, Brown University, Rutgers, The State University of New Jersey, Duke University, Colorado State University, Cooperative Institute for Research in the Atmosphere, University of Utah, Geological Survey of Denmark and Greenland, University of Colorado Boulder, University of Oregon, University of Wyoming
Language: English
Subfield: Atmospheric Science
Field: Earth and Planetary Sciences
Domain: Physical Sciences
SDG: Climate action
Open Access status: gold
Estimated APC paid: $6,990
Awards: NEGATIVE SURFACE MASS BALANCE (SMB) ATTRIBUTED TO INCREASED MELTWATER RUNOFF ACCOUNTS FOR OVER HALF OF THE GREENLAND ICE SHEET (GRIS) CONTRIBUTION TO GLOBAL SEA LEVEL RISE. ESTIMATES OF GRIS SEA LEVEL RISE SMB CONTRIBUTIONS HOWEVER ARE BASED ON REGIONAL CLIMATE MODEL (RCM) PREDICTIONS WHICH INSTANTLY CREDIT ABLATION-ZONE MELTWATER TO THE GLOBAL OCEAN WITHOUT CONSIDERATION OF MELTWATER RETENTION OR TRANSPORT PROCESSES OPERATING ON THE BARE ICE SURFACE. WIDESPREAD EVIDENCE OF COMPLEX FLUVIAL HYDROLOGIC PROCESSES AND MELTWATER RETENTION IN THE ABLATION ZONE SUGGESTS THESE REPRESENTATIONS ARE IMPORTANT. OUTSIDE OF GREENLAND FOR EXAMPLE A PERMEABLE LAYER OF LOW-DENSITY NEAR SURFACE ICE TERMED THE WEATHERING CRUST (WC) HAS BEEN SHOWN TO CONTROL THE DELIVERY OF SURFACE MELTWATER TO SUPRAGLACIAL CHANNELS PROVIDE A SUBSTRATE FOR INTERNAL REFREEZING OF SURFACE MELTWATER AND PREVENT ACCURATE RETRIEVAL OF SMB FROM ICE SURFACE ELEVATION CHANGES. YET VIRTUALLY NOTHING IS KNOWN ABOUT THE SPATIAL EXTENT OF THE GRIS WC OR ITS HYDRAULIC PROPERTIES. WORK PLAN TO ADDRESS THIS KNOWLEDGE GAP THIS RESEARCH WILL USE FIELD AND REMOTE SENSING DATASETS TO ANSWER FOUR SCIENCE QUESTIONS: 1)HOW SPATIALLY EXTENSIVE IS THE WC IN THE SOUTHWEST GRIS ABLATION ZONE? 2)WHAT ARE THE HYDRAULIC AND VISIBLE/NEAR-INFRARED OPTICAL PROPERTIES OF THE WC? 3)HOW MUCH SUBSURFACE MELTWATER AND REFREEZING OCCURS IN THE WC? 4)WHAT IS THE IMPACT OF WC PRESENCE ON RCM AND ALTIMETRIC SMB ESTIMATES? TO ANSWER THESE QUESTIONS WE WILL: 1)MAP THE SPATIAL EXTENT OF THE WC USING NATURALLY OCCURRING CRYOCONITE HOLES AS A PROXY FOR WC PRESENCE. CRYOCONITE HOLES ARE FUNDAMENTALLY DIAGNOSTIC OF WC PRESENCE AND ARE READILY DETECTABLE IN OPTICAL AERIAL IMAGERY. WE WILL USE OPERATION ICEBRIDGE VISIBLE IMAGERY COMBINED WITH LOW ALTITUDE UAS IMAGE ACQUISITION TO MAP CRYOCONITE HOLES IN THE SOUTHWEST GRIS ABLATION ZONE 2)CALCULATE ICE PERMEABILITY USING MEASUREMENTS OF SUBSURFACE WATER TABLE HEIGHT FLUCTUATIONS MEASURED IN CRYOCONITE HOLES AT THREE ELEVATIONS IN THE GRIS ABLATION ZONE TO QUANTIFY SPATIAL VARIABILITY IN WC PERMEABILITY 3)PARAMETERIZE A PHYSICAL MODEL OF WC EVOLUTION TO QUANTIFY SUBSURFACE MELTING AND INTERNAL REFREEZING IN THE WC AND THE EFFECT OF THESE PROCESSES ON CHANGES IN ICE SURFACE ELEVATION 4)COMPARE OUR MODEL RESULTS TO RCM CALCULATIONS OF SMB AND ICE SHEET SURFACE ELEVATION CHANGE IN THE SOUTHWEST GRIS ABLATION ZONE AND USE THESE COMPARISONS TO QUANTIFY THE UNCERTAINTY IN ALTIMETRIC SMB CALCULATIONS DUE TO WC PROCESSES JUSTIFICATION TO NASA EARTH SCIENCE SMD: THIS RESEARCH RESPONDS DIRECTLY TO TWO PRIORITY SCIENCE GOALS IN THE NESSF SOLICITATION AND NASA SCIENCE MISSION DIRECTORATE OBJECTIVE 2.2 ADVANCE KNOWLEDGE OF EARTH AS A SYSTEM TO MEET THE CHALLENGES OF ENVIRONMENTAL CHANGE AND TO IMPROVE LIFE ON OUR PLANET : 1)CLIMATE VARIABILITY AND CHANGE IMPROVE THE ABILITY TO PREDICT CLIMATE CHANGES BY BETTER UNDERSTANDING THE ROLES AND INTERACTIONS OF THE OCEAN ATMOSPHERE LAND AND ICE IN THE CLIMATE 2)WATER AND ENERGY CYCLE ENABLE BETTER ASSESSMENT AND MANAGEMENT OF WATER QUALITY AND QUANTITY TO ACCURATELY PREDICT HOW THE GLOBAL WATER CYCLE EVOLVES IN RESPONSE TO CLIMATE CHANGE TO MEET THESE SCIENCE GOALS THE NESSF SOLICITATION ENCOURAGES SOLICITATIONS THAT INCLUDE INTEGRATION OF SATELLITE- AIRCRAFT- AND SURFACEBASED MEASUREMENTS IN CONJUNCTION WITH MODELS AND SIMULATIONS . IN ADDITION THIS RESEARCH RESPONDS DIRECTLY TO THE NASA ICESAT-2 BASELINE SCIENCE REQUIREMENT45: 1)ICESAT-2 SHALL PRODUCE AN ICE SURFACE ELEVATION PRODUCT THAT ENABLES RESOLUTION OF WINTER (ACCUMULATION) AND SUMMER (ABLATION) ICESHEET ELEVATION CHANGE TO 10 CM [TO ALLOW] CALIBRATION OF ATMOSPHERIC MODELS ESTIMATING ACCUMULATION AND ABLATION FROM THE ICE SHEETS, G5581088128, G6787049212, DRAINAGE EFFICIENCY OF THE GREENLAND SUPRAGLACIAL RIVER NETWORK THE PRODUCTION, TRANSPORT, AND EXPORT OF MELTWATER FROM THE SURFACE OF THE GREENLAND
OpenAlex ID: W4414162222