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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

Correlation map of annual NAO with the local (5 km) annual SMB over 1900–2008. (Online version in colour.)
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RSPA20130662F7: Correlation map of annual NAO with the local (5 km) annual SMB over 1900–2008. (Online version in colour.)

Mentions: We hypothesize that the reason for the change in NARMAX model behaviour over the twentieth century, particularly the lag changes, is a combination of changing calving origin of those icebergs reaching 48° N, declining sea ice off Newfoundland [48] and warming sea surface temperatures in the Labrador Sea and Baffin Bay encouraging calving increases [15,49]. We propose that these factors may have led to a switch during the middle years of the century from an earlier, simpler, situation where icebergs tended to originate from southern Greenland (electronic supplementary material, figure S3), and hence reached 48° N quickly enough for there to appear to be no lag in annual terms, to one where there is a greater mix of icebergs originating from more distant western and northwestern Greenland (from where modelled travel times to 48° N are typically 1–3 years; see electronic supplementary material, figure S1), plus some still from southern Greenland. We suggest one reason for this change is the observed decline of about a third in maximum sea-ice area in the Labrador Sea [48] from 1920 to 1970, leading to more icebergs escaping from the sea ice in Baffin Bay, rather than a real change in calving origin. However, recent warming of the LSST (figure 1), and so increased sea temperatures near calving fronts [15,49], is likely to have led to a general increase in average calving rates. In addition, strong local correlation of GrIS SMB and NAO immediately up-glacier from the calving zones (figure 7) supports significant interaction between these variables at this local scale, through atmospheric variability, particularly affecting run-off, which has increased significantly in the last two decades [1], and perhaps basal sliding rates near the glacier front. The rise in importance, in models of I48N, of SMB in recent decades, shown in figures 5 and 6, is also consistent with a climatically driven increase in calving, through more run-off favouring faster outlet flow [50–52]. Combining these factors, it is likely that there has been a general increase in average calving rates in recent decades, as suggested by the I48N record of figure 2.Figure 7.


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)

Correlation map of annual NAO with the local (5 km) annual SMB over 1900–2008. (Online version in colour.)
© Copyright Policy - open-access
Related In: Results  -  Collection

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

RSPA20130662F7: Correlation map of annual NAO with the local (5 km) annual SMB over 1900–2008. (Online version in colour.)
Mentions: We hypothesize that the reason for the change in NARMAX model behaviour over the twentieth century, particularly the lag changes, is a combination of changing calving origin of those icebergs reaching 48° N, declining sea ice off Newfoundland [48] and warming sea surface temperatures in the Labrador Sea and Baffin Bay encouraging calving increases [15,49]. We propose that these factors may have led to a switch during the middle years of the century from an earlier, simpler, situation where icebergs tended to originate from southern Greenland (electronic supplementary material, figure S3), and hence reached 48° N quickly enough for there to appear to be no lag in annual terms, to one where there is a greater mix of icebergs originating from more distant western and northwestern Greenland (from where modelled travel times to 48° N are typically 1–3 years; see electronic supplementary material, figure S1), plus some still from southern Greenland. We suggest one reason for this change is the observed decline of about a third in maximum sea-ice area in the Labrador Sea [48] from 1920 to 1970, leading to more icebergs escaping from the sea ice in Baffin Bay, rather than a real change in calving origin. However, recent warming of the LSST (figure 1), and so increased sea temperatures near calving fronts [15,49], is likely to have led to a general increase in average calving rates. In addition, strong local correlation of GrIS SMB and NAO immediately up-glacier from the calving zones (figure 7) supports significant interaction between these variables at this local scale, through atmospheric variability, particularly affecting run-off, which has increased significantly in the last two decades [1], and perhaps basal sliding rates near the glacier front. The rise in importance, in models of I48N, of SMB in recent decades, shown in figures 5 and 6, is also consistent with a climatically driven increase in calving, through more run-off favouring faster outlet flow [50–52]. Combining these factors, it is likely that there has been a general increase in average calving rates in recent decades, as suggested by the I48N record of figure 2.Figure 7.

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