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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

Computed contributions to the annual iceberg numbers over 1900–2008 of: (a) the lags of SMB, (b) NAO and (c) LSST. These lags are based on the ERR values for a 30 year sliding window, incremented 1 year at a time, where only one variable was considered as the input. To avoid inconsistencies due to initial and final conditions in the dataset, the initial (before 1915) and final (after 1993) ERR contributions were ignored because of insufficient samples.
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RSPA20130662F6: Computed contributions to the annual iceberg numbers over 1900–2008 of: (a) the lags of SMB, (b) NAO and (c) LSST. These lags are based on the ERR values for a 30 year sliding window, incremented 1 year at a time, where only one variable was considered as the input. To avoid inconsistencies due to initial and final conditions in the dataset, the initial (before 1915) and final (after 1993) ERR contributions were ignored because of insufficient samples.

Mentions: To explore this further, the relative importance of the different time lags in the NARMAX model and how this varied during the twentieth century were examined (figure 6). For much of the twentieth century, SMB has an important component with no lag, alternating, until 1980, with one of 2 years. For the rest of the century, the 1 year lag becomes consistently important. By contrast, the LSST shows a mix of lags during the long period where its overall importance is small, although with more signal in longer lags, but then, when it becomes a major part of the model after the mid-1950s, a strong signal at 0, 1 and sometimes 2 year lags. The NAO's contribution has no lag when its contribution is strongest, during the 1930s to 1950s, but is generally mixed at other times, except for the last few decades, when a 1 year time lag is often dominant. Thus, in the first half of the twentieth century, annual variation in the late spring peak of I48N was controlled by the GrIS SMB of the previous winter, or that two winters before (see figure 6, SMB panel). As suggested by the example shown in table 1 for the sliding window 1900–1929, the dominant relationship at that time tended towards a simple, linear dependence on SMB. However, in the last few decades, the dominant influences have switched to a mix of nonlinear terms, with lags up to 2 years, but with major contributions from 0 and 1 year lags.Figure 6.


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)

Computed contributions to the annual iceberg numbers over 1900–2008 of: (a) the lags of SMB, (b) NAO and (c) LSST. These lags are based on the ERR values for a 30 year sliding window, incremented 1 year at a time, where only one variable was considered as the input. To avoid inconsistencies due to initial and final conditions in the dataset, the initial (before 1915) and final (after 1993) ERR contributions were ignored because of insufficient samples.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

RSPA20130662F6: Computed contributions to the annual iceberg numbers over 1900–2008 of: (a) the lags of SMB, (b) NAO and (c) LSST. These lags are based on the ERR values for a 30 year sliding window, incremented 1 year at a time, where only one variable was considered as the input. To avoid inconsistencies due to initial and final conditions in the dataset, the initial (before 1915) and final (after 1993) ERR contributions were ignored because of insufficient samples.
Mentions: To explore this further, the relative importance of the different time lags in the NARMAX model and how this varied during the twentieth century were examined (figure 6). For much of the twentieth century, SMB has an important component with no lag, alternating, until 1980, with one of 2 years. For the rest of the century, the 1 year lag becomes consistently important. By contrast, the LSST shows a mix of lags during the long period where its overall importance is small, although with more signal in longer lags, but then, when it becomes a major part of the model after the mid-1950s, a strong signal at 0, 1 and sometimes 2 year lags. The NAO's contribution has no lag when its contribution is strongest, during the 1930s to 1950s, but is generally mixed at other times, except for the last few decades, when a 1 year time lag is often dominant. Thus, in the first half of the twentieth century, annual variation in the late spring peak of I48N was controlled by the GrIS SMB of the previous winter, or that two winters before (see figure 6, SMB panel). As suggested by the example shown in table 1 for the sliding window 1900–1929, the dominant relationship at that time tended towards a simple, linear dependence on SMB. However, in the last few decades, the dominant influences have switched to a mix of nonlinear terms, with lags up to 2 years, but with major contributions from 0 and 1 year lags.Figure 6.

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