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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

A comparison of NMSE values for the 100 surrogate tests (solid line) and the raw I48N data (dashed line).
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RSPA20130662F3: A comparison of NMSE values for the 100 surrogate tests (solid line) and the raw I48N data (dashed line).

Mentions: It is first shown that I48N cannot be generated by a purely stochastic process, but should be treated as being forced by external inputs. To support this argument, we generated 100 surrogate datasets, denoted by I48N(s), from the original raw monthly I48N data by using an amplitude adjusted Fourier-transformed surrogates algorithm [44,45]. For each of the surrogate datasets, a nonlinear auto-regressive moving average (NARMA) model of the form3.1I48N(s)(t)=f(s)(I48N(s)(t−1),I48N(s)(t−2),…,I48N(s)(t−24),e(t−1),…,e(t−24))+e(t)was identified, where f(s)(.) are nonlinear functions corresponding to the s-th surrogate, and e(t) is a noise sequence. The maximum nonlinear degree of the model terms was chosen to be 3. In order to show that I48N is not a purely stochastic process, we calculated the normalized mean squared error (NMSE) for each of the 100 surrogate models. Only three NMSE values out of the 100 surrogate tests are lower than that for the original data (figure 3). This result statistically shows that I48N cannot be a purely stochastic process, even taking into account possible stochastic errors in the variable, and seeking physical causes for its variation is a valid pursuit. For the rest of the paper, we use the annual averaged I48N for clarity.Figure 3.


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)

A comparison of NMSE values for the 100 surrogate tests (solid line) and the raw I48N data (dashed line).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

RSPA20130662F3: A comparison of NMSE values for the 100 surrogate tests (solid line) and the raw I48N data (dashed line).
Mentions: It is first shown that I48N cannot be generated by a purely stochastic process, but should be treated as being forced by external inputs. To support this argument, we generated 100 surrogate datasets, denoted by I48N(s), from the original raw monthly I48N data by using an amplitude adjusted Fourier-transformed surrogates algorithm [44,45]. For each of the surrogate datasets, a nonlinear auto-regressive moving average (NARMA) model of the form3.1I48N(s)(t)=f(s)(I48N(s)(t−1),I48N(s)(t−2),…,I48N(s)(t−24),e(t−1),…,e(t−24))+e(t)was identified, where f(s)(.) are nonlinear functions corresponding to the s-th surrogate, and e(t) is a noise sequence. The maximum nonlinear degree of the model terms was chosen to be 3. In order to show that I48N is not a purely stochastic process, we calculated the normalized mean squared error (NMSE) for each of the 100 surrogate models. Only three NMSE values out of the 100 surrogate tests are lower than that for the original data (figure 3). This result statistically shows that I48N cannot be a purely stochastic process, even taking into account possible stochastic errors in the variable, and seeking physical causes for its variation is a valid pursuit. For the rest of the paper, we use the annual averaged I48N for clarity.Figure 3.

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