Glacial meltwater and primary production as drivers for strong CO&lt;sub&gt;2&lt;/sub&gt; uptake in fjord and coastal waters adjacent to the Greenland Ice Sheet

Abstract. The Greenland Ice Sheet releases large amounts of freshwater, which strongly influences the physical and chemical properties of the adjacent fjord systems and continental shelves. Glacial meltwater input is predicted to increase strongly in the future, but the impact of meltwater on the carbonate dynamics of these productive coastal systems remains largely unquantified. Here we present seasonal observations of the carbonate system in the surface waters of a west Greenland tidewater outlet glacier fjord. Our data reveal a permanent undersaturation of CO2 in the surface layer of the entire fjord and adjacent shelf. The average annual CO2 uptake for the fjord is estimated to 65 g C m−2 yr−1 indicating that the fjord system is a strong sink for CO2. Primary production and the high input of glacial meltwater strongly affect the carbonate system in the Godthåbsfjord system. The largest CO2 uptake occurs near to the ice sheet. High glacial meltwater input during the summer months correlates strongly with high levels of CO2 undersaturation, which can be explained by the non-linear effect of salinity on surface water pCO2 resulting from the mixing of glacial meltwater and ambient fjord water. Our findings hence imply that glacial meltwater may form a major driver for CO2 undersaturation in fjord and coastal waters adjacent to an Ice Sheet.

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Glacial meltwater and primary production are drivers of strong CO<sub>2</sub> uptake in fjord and coastal waters adjacent to the Greenland Ice Sheet

Biogeosciences ◽

10.5194/bg-12-2347-2015 ◽

2015 ◽

Vol 12 (8) ◽

pp. 2347-2363 ◽

Cited By ~ 48

Author(s):

L. Meire ◽

D. H. Søgaard ◽

J. Mortensen ◽

F. J. R. Meysman ◽

K. Soetaert ◽

...

Keyword(s):

Primary Production ◽

Coastal Waters ◽

Ice Sheet ◽

Chemical Properties ◽

Greenland Ice Sheet ◽

Co2 Uptake ◽

Glacial Meltwater ◽

Continental Shelves ◽

Physical And Chemical ◽

The Impact

Abstract. The Greenland Ice Sheet releases large amounts of freshwater, which strongly influences the physical and chemical properties of the adjacent fjord systems and continental shelves. Glacial meltwater input is predicted to strongly increase in the future, but the impact of meltwater on the carbonate dynamics of these productive coastal systems remains largely unquantified. Here we present seasonal observations of the carbonate system over the year 2013 in the surface waters of a west Greenland fjord (Godthåbsfjord) influenced by tidewater outlet glaciers. Our data reveal that the surface layer of the entire fjord and adjacent continental shelf are undersaturated in CO2 throughout the year. The average annual CO2 uptake within the fjord is estimated to be 65 g C m−2 yr−1, indicating that the fjord system is a strong sink for CO2. The largest CO2 uptake occurs in the inner fjord near to the Greenland Ice Sheet and high glacial meltwater input during the summer months correlates strongly with low pCO2 values. This strong CO2 uptake can be explained by the thermodynamic effect on the surface water pCO2 resulting from the mixing of fresh glacial meltwater and ambient saline fjord water, which results in a CO2 uptake of 1.8 mg C kg−1 of glacial ice melted. We estimated that 28% of the CO2 uptake can be attributed to the input of glacial meltwater, while the remaining part is due to high primary production. Our findings imply that glacial melt\\-water is an important driver for undersaturation in CO2 in fjord and coastal waters adjacent to large ice sheets.

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Early Holocene ocean conditions off the Zachariæ Isstrøm, Northeast Greenland

10.5194/egusphere-egu21-15076 ◽

2021 ◽

Author(s):

Joanna Davies ◽

Anders Møller Mathiasen ◽

Kristiane Kristensen ◽

Christof Pearce ◽

Marit-Solveig Seidenkrantz

Keyword(s):

Climate Change ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Atlantic Water ◽

The Arctic ◽

Future Climate Change ◽

Polar Regions ◽

Ice Shelf ◽

Outlet Glacier ◽

The Impact

<p>The polar regions exhibit some of the most visible signs of climate change globally; annual mass loss from the Greenland Ice Sheet (GrIS) has quadrupled in recent decades, from 51 &#177; 65 Gt yr<sup>&#8722;1</sup> (1992-2001) to 211 &#177; 37 Gt yr<sup>&#8722;1</sup> (2002-2011). This can partly be attributed to the widespread retreat and speed-up of marine-terminating glaciers. The Zachariae Isstr&#248;m (ZI) is an outlet glacier of the Northeast Greenland Ice Steam (NEGIS), one of the largest ice streams of the GrIS (700km), draining approximately 12% of the ice sheet interior. Observations show that the ZI began accelerating in 2000, resulting in the collapse of the floating ice shelf between 2002 and 2003. By 2014, the ice shelf extended over an area of 52km<sup>2</sup>, a 95% decrease in area since 2002, where it extended over 1040km<sup>2</sup>. Paleo-reconstructions provide an opportunity to extend observational records in order to understand the oceanic and climatic processes governing the position of the grounding zone of marine terminating glaciers and the extent of floating ice shelves. Such datasets are thus necessary if we are to constrain the impact of future climate change projections on the Arctic cryosphere.</p><p>A multi-proxy approach, involving grain size, geochemical, foraminiferal and sedimentary analysis was applied to marine sediment core DA17-NG-ST8-92G, collected offshore of the ZI, on &#160;the Northeast Greenland Shelf. The aim was to reconstruct changes in the extent of the ZI and the palaeoceanographic conditions throughout the Early to Mid Holocene (c.a. 12,500-5,000 cal. yrs. BP). Evidence from the analysis of these datasets indicates that whilst there has been no grounded ice at the site over the last 12,500 years, the ice shelf of the ZI extended as a floating ice shelf over the site between 12,500 and 9,200 cal. yrs. BP, with the grounding line further inland from our study site. This was followed by a retreat in the ice shelf extent during the Holocene Thermal Maximum; this was likely to have been governed, in part, by basal melting driven by Atlantic Water (AW) recirculated from Svalbard or from the Arctic Ocean. Evidence from benthic foraminifera suggest that there was a shift from the dominance of AW to Polar Water at around 7,500 cal. yrs. BP, although the ice shelf did not expand again despite of this cooling of subsurface waters.</p>

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Discharge of debris from ice at the margin of the Greenland ice sheet

Journal of Glaciology ◽

10.3189/172756502781831359 ◽

2002 ◽

Vol 48 (161) ◽

pp. 192-198 ◽

Cited By ~ 21

Author(s):

Peter G. Knight ◽

Richard I. Waller ◽

Carrie J. Patterson ◽

Alison P. Jones ◽

Zoe P. Robinson

Keyword(s):

Ice Sheet ◽

Greenland Ice Sheet ◽

High Rate ◽

Outlet Glacier ◽

Tidewater Glaciers ◽

Sediment Production ◽

Basal Ice ◽

Order Of Magnitude ◽

Sediment Transfer ◽

A Minor

AbstractSediment production at a terrestrial section of the ice-sheet margin in West Greenland is dominated by debris released through the basal ice layer. The debris flux through the basal ice at the margin is estimated to be 12–45 m3 m−1 a−1. This is three orders of magnitude higher than that previously reported for East Antarctica, an order of magnitude higher than sites reported from in Norway, Iceland and Switzerland, but an order of magnitude lower than values previously reported from tidewater glaciers in Alaska and other high-rate environments such as surging glaciers. At our site, only negligible amounts of debris are released through englacial, supraglacial or subglacial sediment transfer. Glaciofluvial sediment production is highly localized, and long sections of the ice-sheet margin receive no sediment from glaciofluvial sources. These findings differ from those of studies at more temperate glacial settings where glaciofluvial routes are dominant and basal ice contributes only a minor percentage of the debris released at the margin. These data on debris flux through the terrestrial margin of an outlet glacier contribute to our limited knowledge of debris production from the Greenland ice sheet.

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Tracing glacial meltwater from the Greenland Ice Sheet to the ocean using gliders

10.1002/essoar.10506220.1 ◽

2021 ◽

Author(s):

Katharine Hendry ◽

Nathan Briggs ◽

Stephanie Anne Henson ◽

Jacob Opher ◽

J. Alexander Brearley ◽

...

Keyword(s):

Ice Sheet ◽

Greenland Ice Sheet ◽

Glacial Meltwater

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Greenland land-terminating glaciers velocity trends during the last two decades

10.5194/egusphere-egu21-2084 ◽

2021 ◽

Author(s):

Paul Halas ◽

Jeremie Mouginot ◽

Basile de Fleurian ◽

Petra Langebroek

Keyword(s):

Water Pressure ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Surface Melting ◽

Limited Area ◽

Ice Dynamics ◽

Basal Sliding ◽

Surface Melt ◽

Ice Sheet Dynamics ◽

The Impact

<div> <p>Ice losses from the Greenland Ice Sheet have been increasing in the last two decades, leading to a larger contribution to the global sea level rise.&#160;Roughly 40% of the contribution comes from ice-sheet dynamics, mainly regulated by basal sliding.&#160;The sliding component&#160;of glaciers has been observed to be strongly related to surface melting, as water&#160;can eventually&#160;reach the bed and impact&#160;the subglacial water pressure, affecting the basal sliding.&#160;&#160;</p> </div><div> <p>The link between ice velocities and surface melt on multi-annual time scale is still not totally understood&#160;even though it&#160;is of major importance with expected increasing surface melting.&#160;Several studies showed&#160;some&#160;correlation between an increase in surface melt and a slowdown in&#160;velocities, but&#160;there is no&#160;consensus&#160;on those trends.&#160;Moreover&#160;those&#160;investigations&#160;only&#160;presented results&#160;in a limited area over&#160;Southwest&#160;Greenland.&#160;&#160;</p> </div><div> <p>Here we present the ice motion over many land-terminating glaciers on the Greenland Ice Sheet for the period 2000 - 2020. This type of glacier is ideal for studying processes at the interface between the bed and the ice since they are exempted from interactions with the sea while still being relevant for all glaciers since they share the same basal friction laws. The velocity data was obtained using optical Landsat 7 & 8 imagery and feature-tracking algorithm. We attached importance keeping the starting date of our image pairs similar, and avoided stacking pairs starting before and after melt seasons, resulting in multiple velocity products for each year.&#160;&#160;</p> </div><div> <p>Our results show similar velocity trends for previously studied areas with a slowdown until 2012 followed by an acceleration.&#160;This trend however does not seem to be observed on the whole ice sheet and is probably&#160;specific&#160;to&#160;this region&#8217;s&#160;climate forcing.&#160;</p> </div><div> <p>Moreover comparison between ice velocities from different parts of Greenland allows us to observe the impact of different climatic trends on ice dynamics.</p> </div>

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Last Interglacial climate and sea-level evolution from a coupled ice sheet–climate model

Climate of the Past ◽

10.5194/cp-12-2195-2016 ◽

2016 ◽

Vol 12 (12) ◽

pp. 2195-2213 ◽

Cited By ~ 22

Author(s):

Heiko Goelzer ◽

Philippe Huybrechts ◽

Marie-France Loutre ◽

Thierry Fichefet

Keyword(s):

Surface Temperature ◽

Sea Level ◽

Ice Sheets ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Last Interglacial ◽

A Minor ◽

The Antarctic ◽

The Impact ◽

And Sea Level

Abstract. As the most recent warm period in Earth's history with a sea-level stand higher than present, the Last Interglacial (LIG, ∼  130 to 115 kyr BP) is often considered a prime example to study the impact of a warmer climate on the two polar ice sheets remaining today. Here we simulate the Last Interglacial climate, ice sheet, and sea-level evolution with the Earth system model of intermediate complexity LOVECLIM v.1.3, which includes dynamic and fully coupled components representing the atmosphere, the ocean and sea ice, the terrestrial biosphere, and the Greenland and Antarctic ice sheets. In this setup, sea-level evolution and climate–ice sheet interactions are modelled in a consistent framework.Surface mass balance change governed by changes in surface meltwater runoff is the dominant forcing for the Greenland ice sheet, which shows a peak sea-level contribution of 1.4 m at 123 kyr BP in the reference experiment. Our results indicate that ice sheet–climate feedbacks play an important role to amplify climate and sea-level changes in the Northern Hemisphere. The sensitivity of the Greenland ice sheet to surface temperature changes considerably increases when interactive albedo changes are considered. Southern Hemisphere polar and sub-polar ocean warming is limited throughout the Last Interglacial, and surface and sub-shelf melting exerts only a minor control on the Antarctic sea-level contribution with a peak of 4.4 m at 125 kyr BP. Retreat of the Antarctic ice sheet at the onset of the LIG is mainly forced by rising sea level and to a lesser extent by reduced ice shelf viscosity as the surface temperature increases. Global sea level shows a peak of 5.3 m at 124.5 kyr BP, which includes a minor contribution of 0.35 m from oceanic thermal expansion. Neither the individual contributions nor the total modelled sea-level stand show fast multi-millennial timescale variations as indicated by some reconstructions.

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The Holocene thermal maximum in the Nordic Seas: the impact of Greenland Ice Sheet melt and other forcings in a coupled atmosphere–sea-ice–ocean model

Climate of the Past ◽

10.5194/cp-9-1629-2013 ◽

2013 ◽

Vol 9 (4) ◽

pp. 1629-1643 ◽

Cited By ~ 23

Author(s):

M. Blaschek ◽

H. Renssen

Keyword(s):

Ice Sheet ◽

Greenland Ice Sheet ◽

Early Holocene ◽

Surface Cooling ◽

Holocene Climate ◽

Nordic Seas ◽

The Holocene ◽

Holocene Thermal Maximum ◽

Thermal Maximum ◽

The Impact

Abstract. The relatively warm early Holocene climate in the Nordic Seas, known as the Holocene thermal maximum (HTM), is often associated with an orbitally forced summer insolation maximum at 10 ka BP. The spatial and temporal response recorded in proxy data in the North Atlantic and the Nordic Seas reveals a complex interaction of mechanisms active in the HTM. Previous studies have investigated the impact of the Laurentide Ice Sheet (LIS), as a remnant from the previous glacial period, altering climate conditions with a continuous supply of melt water to the Labrador Sea and adjacent seas and with a downwind cooling effect from the remnant LIS. In our present work we extend this approach by investigating the impact of the Greenland Ice Sheet (GIS) on the early Holocene climate and the HTM. Reconstructions suggest melt rates of 13 mSv for 9 ka BP, which result in our model in an ocean surface cooling of up to 2 K near Greenland. Reconstructed summer SST gradients agree best with our simulation including GIS melt, confirming that the impact of the early Holocene GIS is crucial for understanding the HTM characteristics in the Nordic Seas area. This implies that modern and near-future GIS melt can be expected to play an active role in the climate system in the centuries to come.

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Seasonal mass variations show timing and magnitude of meltwater storage in the Greenland Ice Sheet

The Cryosphere ◽

10.5194/tc-12-2981-2018 ◽

2018 ◽

Vol 12 (9) ◽

pp. 2981-2999 ◽

Cited By ~ 6

Author(s):

Jiangjun Ran ◽

Miren Vizcaino ◽

Pavel Ditmar ◽

Michiel R. van den Broeke ◽

Twila Moon ◽

...

Keyword(s):

Mass Balance ◽

Climate Model ◽

Spatial Scales ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Surface Mass Balance ◽

High Accumulation ◽

Outlet Glacier ◽

Surface Mass ◽

Meltwater Runoff

Abstract. The Greenland Ice Sheet (GrIS) is currently losing ice mass. In order to accurately predict future sea level rise, the mechanisms driving the observed mass loss must be better understood. Here, we combine data from the satellite gravimetry mission Gravity Recovery and Climate Experiment (GRACE), surface mass balance (SMB) output of the Regional Atmospheric Climate Model v. 2 (RACMO2), and ice discharge estimates to analyze the mass budget of Greenland at various temporal and spatial scales. We find that the mean rate of mass variations in Greenland observed by GRACE was between −277 and −269 Gt yr−1 in 2003–2012. This estimate is consistent with the sum (i.e., -304±126 Gt yr−1) of individual contributions – surface mass balance (SMB, 216±122 Gt yr−1) and ice discharge (520±31 Gt yr−1) – and with previous studies. We further identify a seasonal mass anomaly throughout the GRACE record that peaks in July at 80–120 Gt and which we interpret to be due to a combination of englacial and subglacial water storage generated by summer surface melting. The robustness of this estimate is demonstrated by using both different GRACE-based solutions and different meltwater runoff estimates (namely, RACMO2.3, SNOWPACK, and MAR3.9). Meltwater storage in the ice sheet occurs primarily due to storage in the high-accumulation regions of the southeast and northwest parts of Greenland. Analysis of seasonal variations in outlet glacier discharge shows that the contribution of ice discharge to the observed signal is minor (at the level of only a few gigatonnes) and does not explain the seasonal differences between the total mass and SMB signals. With the improved quantification of meltwater storage at the seasonal scale, we highlight its importance for understanding glacio-hydrological processes and their contributions to the ice sheet mass variability.

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Sensitivity of Greenland Ice Sheet Projections to Model Formulations

Journal of Glaciology ◽

10.3189/2013jog12j182 ◽

2013 ◽

Vol 59 (216) ◽

pp. 733-749 ◽

Cited By ~ 87

Author(s):

H. Goelzer ◽

P. Huybrechts ◽

J.J. Fürst ◽

F.M. Nick ◽

M.L. Andersen ◽

...

Keyword(s):

Regional Climate Model ◽

Sea Level ◽

Flow Model ◽

Climate Model ◽

Regional Climate ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Ice Flow ◽

Outlet Glacier ◽

Glacier Dynamics

AbstractPhysically based projections of the Greenland ice sheet contribution to future sea-level change are subject to uncertainties of the atmospheric and oceanic climatic forcing and to the formulations within the ice flow model itself. Here a higher-order, three-dimensional thermomechanical ice flow model is used, initialized to the present-day geometry. The forcing comes from a high-resolution regional climate model and from a flowline model applied to four individual marine-terminated glaciers, and results are subsequently extended to the entire ice sheet. The experiments span the next 200 years and consider climate scenario SRES A1B. The surface mass-balance (SMB) scheme is taken either from a regional climate model or from a positive-degree-day (PDD) model using temperature and precipitation anomalies from the underlying climate models. Our model results show that outlet glacier dynamics only account for 6–18% of the sea-level contribution after 200 years, confirming earlier findings that stress the dominant effect of SMB changes. Furthermore, interaction between SMB and ice discharge limits the importance of outlet glacier dynamics with increasing atmospheric forcing. Forcing from the regional climate model produces a 14–31 % higher sea-level contribution compared to a PDD model run with the same parameters as for IPCC AR4.

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Heterogeneous CO<sub>2</sub> and CH<sub>4</sub> content of glacial meltwater from the Greenland Ice Sheet and implications for subglacial carbon processes

The Cryosphere ◽

10.5194/tc-15-1627-2021 ◽

2021 ◽

Vol 15 (3) ◽

pp. 1627-1644

Author(s):

Andrea J. Pain ◽

Jonathan B. Martin ◽

Ellen E. Martin ◽

Åsa K. Rennermalm ◽

Shaily Rahman

Keyword(s):

Greenhouse Gas ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Mineral Weathering ◽

Atmospheric Co2 ◽

The Arctic ◽

Co2 Concentrations ◽

Geochemical Models ◽

Atmospheric Co2 Concentrations ◽

The Impact

Abstract. Accelerated melting of the Greenland Ice Sheet has increased freshwater delivery to the Arctic Ocean and amplified the need to understand the impact of Greenland Ice Sheet meltwater on Arctic greenhouse gas budgets. We evaluate subglacial discharge from the Greenland Ice Sheet for carbon dioxide (CO2) and methane (CH4) concentrations and δ13C values and use geochemical models to evaluate subglacial CH4 and CO2 sources and sinks. We compare discharge from southwest (a sub-catchment of the Isunnguata Glacier, sub-Isunnguata, and the Russell Glacier) and southern Greenland (Kiattut Sermiat). Meltwater CH4 concentrations vary by orders of magnitude between sites and are saturated with respect to atmospheric concentrations at Kiattut Sermiat. In contrast, meltwaters from southwest sites are supersaturated, even though oxidation reduces CH4 concentrations by up to 50 % during periods of low discharge. CO2 concentrations range from supersaturated at sub-Isunnguata to undersaturated at Kiattut Sermiat. CO2 is consumed by mineral weathering throughout the melt season at all sites; however, differences in the magnitude of subglacial CO2 sources result in meltwaters that are either sources or sinks of atmospheric CO2. At the sub-Isunnguata site, the predominant source of CO2 is organic matter (OM) remineralization. However, multiple or heterogeneous subglacial CO2 sources maintain atmospheric CO2 concentrations at Russell but not at Kiattut Sermiat, where CO2 is undersaturated. These results highlight a previously unrecognized degree of heterogeneity in greenhouse gas dynamics under the Greenland Ice Sheet. Future work should constrain the extent and controls of heterogeneity to improve our understanding of the impact of Greenland Ice Sheet melt on Arctic greenhouse gas budgets, as well as the role of continental ice sheets in greenhouse gas variations over glacial–interglacial timescales.

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