Antarctic icebergs reorganize ocean circulation during Pleistocene glacials

Starr, Aidan; Hall, Ian R; Barker, Stephen; Rackow, Thomas; Zhang, Xu; Hemming, S. R.; Lubbe, Jeroen van der; Knorr, Gregor; Berke, Melissa A.; Bigg, Grant R.; Cartagena‐Sierra, A.; Jiménez-Espejo, Francisco Jose; Gong, Xun; Gruetzner, Jens; Lathika, N.; LeVay, Leah J.; Robinson, Rebecca S.; Ziegler, Martin

doi:10.1038/s41586-020-03094-7

Cited by 39 publications

(62 citation statements)

References 94 publications

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“…Model results suggest that enlargement of the Antarctic ice sheet could lead directly to a strengthening of the AMOC (Shi et al., 2020). Moreover, recent evidence (Starr et al., 2021) suggests that iceberg calving around Antarctica may have increased from ∼1.2 Ma, lending support to the idea that the Antarctic ice sheet increased its marine‐based status at that time.…”

Section: Resultsmentioning

confidence: 88%

“…Model results suggest that enlargement of the Antarctic ice sheet could lead directly to a strengthening of the AMOC (Shi et al, 2020). Moreover, recent evidence (Starr et al, 2021) suggests that iceberg calving around Antarctica may have increased from ∼1.2 Ma, lending support to the idea that the Antarctic ice sheet increased its marine-based status at that time. An alternative explanation for why the Atlantic Inflow may have strengthened over the past million years or so implicates variations in the depth of the Greenland-Scotland Ridge (GSR) as a function of the Iceland mantle plume.…”

Section: Possible Controls On the Nordic Heat Pumpmentioning

confidence: 79%

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Strengthening Atlantic Inflow Across the Mid‐Pleistocene Transition

Barker

Zhang

Jonkers

et al. 2021

Paleoceanog and Paleoclimatol

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First '100kyr' glacial cycle preceded Marine Isotope Stage 25 (~0.95Ma) • Increasing Atlantic Inflow could promote ice sheet growth given pre-existence of moderately sized ice sheets Accepted ArticleThis article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as

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Section: Resultsmentioning

confidence: 88%

Section: Possible Controls On the Nordic Heat Pumpmentioning

confidence: 79%

Strengthening Atlantic Inflow Across the Mid‐Pleistocene Transition

Barker

Zhang

Jonkers

et al. 2021

Paleoceanog and Paleoclimatol

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“…Hence, the westward drift of this iceberg mainly represents the sea current along the Amundsen Sea to the Ross Sea. In the coastal regions of the Amundsen Sea and the Ross Sea, the ocean circulation is dominated by the westward Antarctic Coastal Current (ACoC), which is mainly driven by wind stress and buoyancy (Whitworth et al, 1985;Orsi et al, 1995;Mathiot et al, 2011;Kim et al, 2016;Stern et al, 2016).…”

Section: Trajectory Of the Icebergmentioning

confidence: 99%

“…), icebergs provide important insights for the interaction of these variables (Schodlok et al, 2006). In addition, the formation and melting of icebergs influence global climate (Romanov et al, 2008;Mackie et al, 2020), ocean flux (Silva et al, 2006;Rackow et al, 2017;Starr et al, 2021), sea ice production (Martin et al, 2007;Merino et al, 2016), dissolved iron concentration (Lin et al, 2011;De Jong et al, 2015), and ecosystems and biology (Wilson et al, 2016;Schwarz and Schodlok, 2009;Biddle et al, 2015). Furthermore, icebergs can threaten ship navigation (Lasserre, 2015).…”

Section: Introductionmentioning

confidence: 99%

Semi-automated tracking of iceberg B43 using Sentinel-1 SAR images via Google Earth Engine

et al. 2021

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Abstract. Sentinel-1 C-band synthetic aperture radar (SAR) images can be used to observe the drift of icebergs over the Southern Ocean with around 1–3 d of temporal resolution and 10–40 m of spatial resolution. The Google Earth Engine (GEE) cloud-based platform allows processing of a large quantity of Sentinel-1 images, saving time and computational resources. In this study, we process Sentinel-1 data via GEE to detect and track the drift of iceberg B43 during its lifespan of 3 years (2017–2020) in the Southern Ocean. First, to detect all candidate icebergs in Sentinel-1 images, we employ an object-based image segmentation (simple non-iterative clustering – SNIC) and a traditional backscatter threshold method. Next, we automatically choose and trace the location of the target iceberg by comparing the centroid distance histograms (CDHs) of all detected icebergs in subsequent days with the CDH of the reference target iceberg. Using this approach, we successfully track iceberg B43 from the Amundsen Sea to the Ross Sea and examine its changes in area, speed, and direction. Three periods with sudden losses of area (i.e., split-offs) coincide with periods of low sea ice concentration, warm air temperature, and high waves. This implies that these variables may be related to mechanisms causing the split-off of the iceberg. Since the iceberg is generally surrounded by compacted sea ice, its drift correlates in part with sea ice motion and wind velocity. Given that the bulk of the iceberg is under water (∼30–60 m freeboard and ∼150–400 m thickness), its motion is predominantly driven by the westward-flowing Antarctic Coastal Current, which dominates the circulation of the region. Considering the complexity of modeling icebergs, there is a demand for a large iceberg database to better understand the behavior of icebergs and their interactions with surrounding environments. The semi-automated iceberg tracking based on the storage capacity and computing power of GEE can be used for this purpose.

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“…For this reason, it is important to study the AMOC response in a freshwater discharge scenario that accounts for both Northern and Southern Hemisphere sources instead of meltwater discharge from Greenland only (Swingedouw et al 2013;Weijer et al 2012;Bakker et al 2016;Haskins et al 2020). The calving of icebergs affects spatial patterns of the mass redistribution, especially in the Southern Ocean (Starr et al 2021).…”

Section: Introductionmentioning

confidence: 99%

Circulation adjustment in the Arctic and Atlantic in response to Greenland and Antarctic mass loss

2021

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Following a high-end projection for mass loss from the Greenland and Antarctic ice-sheets, a freshwater forcing was applied to the ocean surface in the coupled climate model EC-Earthv2.2 to study the response to meltwater release assuming an RCP8.5 emission scenario. The meltwater forcing results in an overall freshening of the Atlantic that is dominated by advective changes, strongly enhancing the freshening due to dilution by Greenland meltwater release. The strongest circulation change occurs in the western North Atlantic subpolar gyre and in the gyre in the Nordic Seas, leaving the North Atlantic subpolar gyre the region where most advective salt export occurs. Associated with counteracting changes in both gyre systems, the response of the Atlantic Meridional Overturning Circulation is rather weak over the 190 years of the experiment; it reduces with only 1 Sv ($$= 10^6$$ = 10 6 m $$^3$$ 3 s $$^{-1}$$ - 1 ), compared to changes in the subpolar gyre of 5 Sv. This relative insensitivity of the AMOC to the forcing is attributed to enhanced convection in the Nordic Seas and stronger overflows that compensate reduced convection in the Labrador and Irminger Seas, and lead to higher sea surface temperatures (SSTs) in the former and lower SSTs in the latter region. The weakened subpolar gyre in the west also shifts the North Atlantic Current and the subpolar-subtropical gyre boundary; with the subtropical gyre expanding, and the western subpolar gyre contracting. The SST changes are associated with obduction of Atlantic waters in the Nordic Seas that would otherwise obduct in the western subpolar gyre. The anomalous SSTs also induce a coupled ocean-atmosphere feedback that further strengthens the Nordic Seas circulation and weakens the western subpolar gyre. This occurs because the anomalous SST-gradient enhances the westerlies, especially between 65$$^{\circ }$$ ∘ N and 70$$^{\circ }$$ ∘ N; the associated increase in windstress curl consequently enhances the gyre in the Nordic Seas. This feedback is driven by the Greenland mass loss; Antarctic meltwater discharge causes a weaker, opposite response and more particularly affects the South Atlantic salinity budget through northward advection of low-salinity waters from the Southern Ocean. This effect, however, becomes visible only hundred years after the onset of Antarctic mass loss. We conclude that the response to freshwater forcing from both ice caps can lead to a complex response in the Atlantic circulation systems with opposing effects in different subbasins. The relative strength of the response is time-dependent and largely governed by internal feedbacks; the forcing acts mainly as a trigger and is decoupled from the response.

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Antarctic icebergs reorganize ocean circulation during Pleistocene glacials

Cited by 39 publications

References 94 publications

Strengthening Atlantic Inflow Across the Mid‐Pleistocene Transition

Strengthening Atlantic Inflow Across the Mid‐Pleistocene Transition

Semi-automated tracking of iceberg B43 using Sentinel-1 SAR images via Google Earth Engine

Circulation adjustment in the Arctic and Atlantic in response to Greenland and Antarctic mass loss

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