The role of ocean dynamics in king penguin range estimation

Antarctic ice cores show that a millennial-scale cooling event, the Antarctic Cold Reversal (14,700 to 13,000 years ago), interrupted the last deglaciation 1–3. The Antarctic Cold Reversal coincides with the Bølling–Allerød warm stage in the North Atlantic, providing an example of the inter-hemispheric coupling of abrupt climate change generally referred to as the bipolar seesaw 4–9. However, the ocean–atmosphere dynamics governing this coupling are debated 10–15. Here we examine the extent and expression of the Antarctic Cold Reversal in the Southern Hemisphere using a synthesis of 84 palaeoclimate records. We find that the cooling is strongest in the South Atlantic and all regions south of 40 • S. At the same time, the terrestrial tropics and subtropics show abrupt hydrologic variations that are significantly correlated with North Atlantic climate changes. Our transient global climate model simulations indicate that the observed extent of Antarctic Cold Reversal cooling can be explained by enhanced northward ocean heat transport from the South to North Atlantic 10 , amplified by the expansion and thickening of sea ice in the Southern Ocean. The hydrologic variations at lower latitudes result from an opposing enhancement of southward heat transport in the atmosphere mediated by the Hadley circulation. Our findings reconcile previous arguments about the relative dominance of ocean 5,10,11 and atmospheric 14,15 heat transports in inter-hemispheric coupling, demonstrating that the spatial pattern of past millennial-scale climate change reflects the superposition of both.

Ecological Monographs, 2010

We assess the response of pack ice penguins, Emperor (Aptenodytes forsteri) and Ade´lie (Pygoscelis adeliae), to habitat variability and, then, by modeling habitat alterations, the qualitative changes to their populations, size and distribution, as Earth's average tropospheric temperature reaches 28C above preindustrial levels (ca. 1860), the benchmark set by the European Union in efforts to reduce greenhouse gases. First, we assessed models used in the Intergovernmental Panel on Climate Change Fourth Assessment Report (AR4) on penguin performance duplicating existing conditions in the Southern Ocean. We chose four models appropriate for gauging changes to penguin habitat: GFDL-CM2.1, GFDL-CM2.0, MIROC3.2(hi-res), and MRI-CGCM2.3.2a. Second, we analyzed the composited model ENSEMBLE to estimate the point of 28C warming (2025-2052) and the projected changes to sea ice coverage (extent, persistence, and concentration), sea ice thickness, wind speeds, precipitation, and air temperatures. Third, we considered studies of ancient colonies and sediment cores and some recent modeling, which indicate the (space/time) large/centennialscale penguin response to habitat limits of all ice or no ice. Then we considered results of statistical modeling at the temporal interannual-decadal scale in regard to penguin response over a continuum of rather complex, meso-to large-scale habitat conditions, some of which have opposing and others interacting effects. The ENSEMBLE meso/decadal-scale output projects a marked narrowing of penguins' zoogeographic range at the 28C point. Colonies north of 708 S are projected to decrease or disappear: ;50% of Emperor colonies (40% of breeding population) and ;75% of Ade´lie colonies (70% of breeding population), but limited growth might occur south of 738 S. Net change would result largely from positive responses to increase in polynya persistence at high latitudes, overcome by decreases in pack ice cover at lower latitudes and, particularly for Emperors, ice thickness. Ade´lie Penguins might colonize new breeding habitat where concentrated pack ice diverges and/or disintegrating ice shelves expose coastline. Limiting increase will be decreased persistence of pack ice north of the Antarctic Circle, as this species requires daylight in its wintering areas. Ade´lies would be affected negatively by increasing snowfall, predicted to increase in certain areas owing to intrusions of warm, moist marine air due to changes in the Polar Jet Stream.

The Cryosphere Discussions, 2015

Future changes in atmospheric circulation and associated modes of variability are a major source of uncertainty in climate projections. Nowhere is this issue more acute than across the mid-to high-latitudes of the Southern Hemisphere (SH) which over the last few decades has experienced extreme and regional variable trends in precipitation, 5 ocean circulation, and temperature, with major implications for Antarctic ice melt and surface mass balance. Unfortunately there is a relative dearth of observational data, limiting our understanding of the driving mechanism(s). Here we report a new 130-year annually-resolved record of δD -a proxy for temperature -from the South Geographic Pole where we find a significant influence from extra-tropical pressure anomalies which 10 act as "gatekeepers" to the meridional exchange of air masses. Reanalysis of global atmospheric circulation suggests these pressure anomalies play a considerably larger influence on mid-to high-latitude SH climate than hitherto believed, modulated by the tropical Pacific Ocean. Our findings suggest that future increasing tropical warmth will strengthen meridional circulation, exaggerating current trends, with potentially 15 significant impacts on Antarctic surface mass balance. 25 decades; while the Peninsula and West Antarctic provide strong evidence for surface 4020 Abstract TCD 9, 4019-4042, 2015 Abstract TCD 9, 4019-4042, 2015 Abstract TCD 9, 4019-4042, 2015 Abstract increased ENSO variability, implying precipitation will continue to decline in southwest 4027

2019

Warming of the Antarctic Peninsula in the latter half of the twentieth century was greater than any other terrestrial environment in the Southern Hemisphere, and clear cryospheric and biological consequences have been observed. Under a global 1.5 • C scenario, warming in the Antarctic Peninsula is likely to increase the number of days above 0 • C, with up to 130 of such days each year in the northern Peninsula. Ocean turbulence will increase, making the circumpolar deep water (CDW) both warmer and shallower, delivering heat to the sea surface and to coastal margins. Thinning and recession of marine margins of glaciers and ice caps is expected to accelerate to terrestrial limits, increasing iceberg production, after which glacier retreat may slow on land. Ice shelves will experience continued increase in meltwater production and consequent structural change, but not imminent regional collapses. Marine biota can respond in multiple ways to climatic changes, with effects complicated by past resource extraction activities. Southward distribution shifts have been observed in multiple taxa during the last century and these are likely to continue. Exposed (ice free) terrestrial areas will expand, providing new habitats for native and non-native organisms, but with a potential loss of genetic diversity. While native terrestrial biota are likely to benefit from modest warming, the greatest threat to native biodiversity is from non-native terrestrial species.

Nature Climate Change, 2019

Future iceberg and meltwater discharge from the Antarctic ice sheet (AIS) could substantially exceed present levels, with strong implications for future climate and sea levels. Recent climate model simulations on the impact of a rapid disintegration of the AIS on climate have applied idealized freshwater forcing scenarios 1,2 rather than the more realistic iceberg forcing. Here we use a coupled climate-iceberg model to determine the climatic effects of combined iceberg latent heat of fusion and freshwater forcing. The iceberg forcing is derived from an ensemble of future simulations conducted using the Penn State ice-sheet model 3. In agreement with previous studies , the simulated AIS meltwater forcing causes a substantial delay in greenhouse warming in the Southern Hemisphere and activates a transient positive feedback between surface freshening , subsurface warming and ice-sheet/shelf melting, which can last for about 100 years and may contribute to an accelerated ice loss around Antarctica. However, accounting further for the oceanic heat loss due to iceberg melting considerably increases the surface cooling effect and reduces the subsur-face temperature feedback amplitude. Our findings document the importance of considering realistic climate-ice sheet-iceberg coupling for future climate and sea-level projections. Recent ice-sheet simulations suggest that future AIS discharge could increase substantially towards the end of this century, attaining values of >1 Sv (1 Sv = 10 6 m 3 s-1 ≈ 31,500 Gt yr-1 ≈ 0.087 m sea-level equivalent (SLE) yr-1) 3-6. With AIS discharge causing reduced Southern Hemisphere surface temperatures 1,7-12 , freshwater forcing of this magnitude could delay Southern Hemisphere greenhouse warming by up to several decades 2. Moreover, AIS discharge has been shown to lead to increased subsurface ocean temperatures around Antarctica, which may provide a positive feedback to AIS melting 1,2,4,6,12-14. Previous simulations have applied either climate forcing to ice-sheet models 3 or ice-sheet freshwater forcing to climate models 2. Important feedbacks among atmosphere, ocean and the AIS are therefore not properly resolved. Moreover, the amplitude of future AIS discharge remains highly uncertain, even in response to specific warming scenarios 15. Processes such as hydrofractur-ing, ice-cliff instability and basal melting are observationally not well constrained 5. Resulting uncertainties translate into uncertainties in global sea-level projections and AIS discharge, which are reflected in substantial discrepancies between different state-of-the-art estimates of future contributions to sea-level changes from the AIS 2,3,5,6,15. Models also do not agree well on the partition between basal melting and calving fluxes 6,16. In more realistic scenarios, calving icebergs are advected by ocean currents and winds, influencing the ocean, sea ice and climate along their trajectories by continuously changing freshwater and heat fluxes 17,18. Iceberg melting is also modulated seasonally, as sea ice, winds, ocean currents and temperatures change dramatically around Antarctica 19. This fundamental process has not been properly included in future climate and sea-level projections. To improve our understanding of the climatic response to future changes in the AIS, we use the earth system model of intermediate complexity (LOVECLIM, see Methods) under the representative concentration pathway (RCP) 4.5 and 8.5 GHG emission scenarios (RCP4.5 and RCP8.5, respectively). We further apply a wide range of freshwater and iceberg forcing scenarios derived from ice-sheet model simulations conducted with the Penn State ice-sheet model 16. The low computational cost of LOVECLIM allows us to conduct a large number of ensemble simulations with varying AIS meltwater/ iceberg discharge amplitude (Fig. 1; Methods). The thermodynamic and dynamic impacts of icebergs are tested by varying the implementation of AIS forcing in different experiments using the same AIS forcing scenario (Supplementary Table 1). Here, the thermo-dynamic effect of icebergs describes the consequences of energy consumption by the melting processes to account for latent heat. Icebergs can travel large distances before melting entirely, thereby generating spatiotemporally varying meltwater patterns that extend across the Southern Ocean 19,20. This process is, henceforth, referred to as the dynamic iceberg effect. To isolate its climatic impact, simulations are compared to idealized experiments with spatially homogeneous freshwater forcing. The oceanic response to Antarctic meltwater discharge is well documented in climate models 1,2,7-12. By freshening the Southern Ocean surface water and lowering its density, AIS meltwater strengthens Southern Ocean stratification 1,7-12. The latter acts as a barrier for deep convection, Antarctic bottom water formation and vertical heat fluxes, enhancing Southern Hemisphere sea-ice production and causing surface cooling and subsurface ocean warming around Antarctica 1,12,21. The impact on global ocean circulation 22-24 then results in an interhemispheric asymmetry in surface temperature 25 , a northward displacement of the intertropical convergence zone and global precipitation changes 22,26,27. The response of LOVECLIM to freshwater forcing 1,6,7 is very similar to that recently reported using more sophisticated coupled general circulation models 2,22. In control experiments with greenhouse forcing, but without AIS forcing, global surface air