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A century of variation in the dependence of Greenland iceberg calving on ice sheet surface mass balance and regional climate change.

Bigg GR, Wei HL, Wilton DJ, Zhao Y, Billings SA, Hanna E, Kadirkamanathan V - Proc. Math. Phys. Eng. Sci. (2014)

Bottom Line: A century-long record of Greenland icebergs comes from the International Ice Patrol's record of icebergs (I48N) passing latitude 48° N, off Newfoundland.I48N exhibits strong interannual variability, with a significant increase in amplitude over recent decades.We also suggest that GrIS calving discharge is episodic on at least a regional scale and has recently been increasing significantly, largely as a result of west Greenland sources.

View Article: PubMed Central - PubMed

Affiliation: Department of Geography , University of Sheffield , Sheffield S10 2TN, UK.

ABSTRACT
Iceberg calving is a major component of the total mass balance of the Greenland ice sheet (GrIS). A century-long record of Greenland icebergs comes from the International Ice Patrol's record of icebergs (I48N) passing latitude 48° N, off Newfoundland. I48N exhibits strong interannual variability, with a significant increase in amplitude over recent decades. In this study, we show, through a combination of nonlinear system identification and coupled ocean-iceberg modelling, that I48N's variability is predominantly caused by fluctuation in GrIS calving discharge rather than open ocean iceberg melting. We also demonstrate that the episodic variation in iceberg discharge is strongly linked to a nonlinear combination of recent changes in the surface mass balance (SMB) of the GrIS and regional atmospheric and oceanic climate variability, on the scale of the previous 1-3 years, with the dominant causal mechanism shifting between glaciological (SMB) and climatic (ocean temperature) over time. We suggest that this is a change in whether glacial run-off or under-ice melting is dominant, respectively. We also suggest that GrIS calving discharge is episodic on at least a regional scale and has recently been increasing significantly, largely as a result of west Greenland sources.

No MeSH data available.


Related in: MedlinePlus

Source region for fine resolution model I48N, with variable yearly discharge, as determined by equation (2.1). Different regions are defined as follows. ‘South’ is from those sources equatorward of 65° N. ‘Mid-west’ denotes releases from between 65° N and 72° N on the west coast of Greenland or Baffin Island (although the latter do not in fact contribute to I48N). ‘Northwest’ refers to icebergs from all other release sites in Baffin Bay, Nares Strait and the Canadian Arctic islands north of 72° N. ‘Other’ is all of eastern Greenland above 65° N plus sites in Svalbard and the Russian Arctic islands.
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RSPA20130662F4: Source region for fine resolution model I48N, with variable yearly discharge, as determined by equation (2.1). Different regions are defined as follows. ‘South’ is from those sources equatorward of 65° N. ‘Mid-west’ denotes releases from between 65° N and 72° N on the west coast of Greenland or Baffin Island (although the latter do not in fact contribute to I48N). ‘Northwest’ refers to icebergs from all other release sites in Baffin Bay, Nares Strait and the Canadian Arctic islands north of 72° N. ‘Other’ is all of eastern Greenland above 65° N plus sites in Svalbard and the Russian Arctic islands.

Mentions: If open ocean circulation and temperature change has not caused the dominant variability in iceberg numbers then there must be some fundamental relationship with iceberg discharge from sources whose icebergs reach 48° N. It is worth noting that this was the implication of a fjordal model study of iceberg sedimentation as well [46], where the glaciological regime was found to be more important than fjordal sea temperature. To confirm this, another experiment was performed, using the same atmospheric forcing, where the annual calving discharge for each Northern Hemisphere glacier was defined by equation (2.1). The resulting model prediction for I48N (variable discharge line in figure 2) shows very high correlation (r=0.83). From the ocean–iceberg modelling, it is found that over 99% of the modelled icebergs crossing 48° N originated from southern or western Greenland fjords, or other glaciers within northern Baffin Bay (figure 4). The ocean model results therefore strongly suggest that variation in Greenland glacial discharge should dominate the underlying fluctuation of I48N. As the largest changes in SMB in recent years have occurred in the ablation zone [47], and therefore around calving glaciers, it is likely that the relatively well-known SMB will be physically related to the poorly known discharge [3]. Previously, it has been shown that there is not a simple linear relationship between SMB and I48N [1]. A more complex, nonlinear relationship between this index, SMB, and parameterizations of regional climatic and local oceanic change, taken as the NAO and LSST, was therefore sought using NARMAX modelling.Figure 4.


A century of variation in the dependence of Greenland iceberg calving on ice sheet surface mass balance and regional climate change.

Bigg GR, Wei HL, Wilton DJ, Zhao Y, Billings SA, Hanna E, Kadirkamanathan V - Proc. Math. Phys. Eng. Sci. (2014)

Source region for fine resolution model I48N, with variable yearly discharge, as determined by equation (2.1). Different regions are defined as follows. ‘South’ is from those sources equatorward of 65° N. ‘Mid-west’ denotes releases from between 65° N and 72° N on the west coast of Greenland or Baffin Island (although the latter do not in fact contribute to I48N). ‘Northwest’ refers to icebergs from all other release sites in Baffin Bay, Nares Strait and the Canadian Arctic islands north of 72° N. ‘Other’ is all of eastern Greenland above 65° N plus sites in Svalbard and the Russian Arctic islands.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4042714&req=5

RSPA20130662F4: Source region for fine resolution model I48N, with variable yearly discharge, as determined by equation (2.1). Different regions are defined as follows. ‘South’ is from those sources equatorward of 65° N. ‘Mid-west’ denotes releases from between 65° N and 72° N on the west coast of Greenland or Baffin Island (although the latter do not in fact contribute to I48N). ‘Northwest’ refers to icebergs from all other release sites in Baffin Bay, Nares Strait and the Canadian Arctic islands north of 72° N. ‘Other’ is all of eastern Greenland above 65° N plus sites in Svalbard and the Russian Arctic islands.
Mentions: If open ocean circulation and temperature change has not caused the dominant variability in iceberg numbers then there must be some fundamental relationship with iceberg discharge from sources whose icebergs reach 48° N. It is worth noting that this was the implication of a fjordal model study of iceberg sedimentation as well [46], where the glaciological regime was found to be more important than fjordal sea temperature. To confirm this, another experiment was performed, using the same atmospheric forcing, where the annual calving discharge for each Northern Hemisphere glacier was defined by equation (2.1). The resulting model prediction for I48N (variable discharge line in figure 2) shows very high correlation (r=0.83). From the ocean–iceberg modelling, it is found that over 99% of the modelled icebergs crossing 48° N originated from southern or western Greenland fjords, or other glaciers within northern Baffin Bay (figure 4). The ocean model results therefore strongly suggest that variation in Greenland glacial discharge should dominate the underlying fluctuation of I48N. As the largest changes in SMB in recent years have occurred in the ablation zone [47], and therefore around calving glaciers, it is likely that the relatively well-known SMB will be physically related to the poorly known discharge [3]. Previously, it has been shown that there is not a simple linear relationship between SMB and I48N [1]. A more complex, nonlinear relationship between this index, SMB, and parameterizations of regional climatic and local oceanic change, taken as the NAO and LSST, was therefore sought using NARMAX modelling.Figure 4.

Bottom Line: A century-long record of Greenland icebergs comes from the International Ice Patrol's record of icebergs (I48N) passing latitude 48° N, off Newfoundland.I48N exhibits strong interannual variability, with a significant increase in amplitude over recent decades.We also suggest that GrIS calving discharge is episodic on at least a regional scale and has recently been increasing significantly, largely as a result of west Greenland sources.

View Article: PubMed Central - PubMed

Affiliation: Department of Geography , University of Sheffield , Sheffield S10 2TN, UK.

ABSTRACT
Iceberg calving is a major component of the total mass balance of the Greenland ice sheet (GrIS). A century-long record of Greenland icebergs comes from the International Ice Patrol's record of icebergs (I48N) passing latitude 48° N, off Newfoundland. I48N exhibits strong interannual variability, with a significant increase in amplitude over recent decades. In this study, we show, through a combination of nonlinear system identification and coupled ocean-iceberg modelling, that I48N's variability is predominantly caused by fluctuation in GrIS calving discharge rather than open ocean iceberg melting. We also demonstrate that the episodic variation in iceberg discharge is strongly linked to a nonlinear combination of recent changes in the surface mass balance (SMB) of the GrIS and regional atmospheric and oceanic climate variability, on the scale of the previous 1-3 years, with the dominant causal mechanism shifting between glaciological (SMB) and climatic (ocean temperature) over time. We suggest that this is a change in whether glacial run-off or under-ice melting is dominant, respectively. We also suggest that GrIS calving discharge is episodic on at least a regional scale and has recently been increasing significantly, largely as a result of west Greenland sources.

No MeSH data available.


Related in: MedlinePlus