Holocene dynamics of the Southern Hemisphere westerly winds and possible links to CO2 outgassing

The Southern Hemisphere westerly winds (SHW) play an important role in regulating the capacity of the Southern Ocean carbon sink. They modulate upwelling of carbon-rich deep water and, with sea ice, determine the ocean surface area available for air–sea gas exchange. Some models indicate that the current strengthening and poleward shift of these winds will weaken the carbon sink. If correct, centennial- to millennial-scale reconstructions of the SHW intensity should be linked with past changes in atmospheric CO2, temperature and sea ice. Here we present a 12,300-year reconstruction of wind strength based on three independent proxies that track inputs of sea-salt aerosols and minerogenic particles accumulating in lake sediments on sub-Antarctic Macquarie Island. Between about 12.1 thousand years ago (ka) and 11.2 ka, and since about 7 ka, the wind intensities were above their long-term mean and corresponded with increasing atmospheric CO2. Conversely, from about 11.2 to 7.2 ka, the wind intensities were below their long-term mean and corresponded with decreasing atmospheric CO2. These observations are consistent with model inferences of enhanced SHW contributing to the long-term outgassing of CO2 from the Southern Ocean

Irregular Migration Theories

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The Study of Irregular Migration

AbstractThe study of irregular migration as a specific social phenomenon took off during the 70s in the US. Since then, the academic interest has continually grown and spread, first to Europe and, in the last years, to other regions worldwide. This interest can certainly be related to the increasing attention paid to the study of migrations more in general (Castles & Miller, 1993). The trend can be linked to those broad and complex social and economic changes, often subsumed under the concept of globalization. The specific focus on irregular migration, though gaining momentum throughout the 1980s, reached preeminent attention in the 1990s. On both sides of the Atlantic, the explosion of the so-called "migration crisis" (Zolberg & Benda, 2001) and the emergence of irregular migration as a widespread social fact raised the attention of public opinion and academics alike. Moreover, in recent years, what seemed at first to be an issue concerning only the high-income regions of the planet, now involves also medium and low-income ones, making irregular migration a truly global structural phenomenon (Cvajner & Sciortino, 2010a; Düvell, 2006)

Late Quaternary changes in the westerly winds over the Southern Ocean – a progress report

The Southern Hemisphere westerly winds (SHW) are the strongest time-averaged oceanic winds. They drive the circulation of the Southern Ocean and changes in their strength and position are thought to modify the upwelling of carbon rich deep water, exerting significant control on the ocean-atmosphere balance of CO2. Thus changes in the SHW, such as the recently observed intensification, could influence whether the Southern Ocean acts as a net source or sink of atmospheric CO2, with major implications for global climate. At present the relationships between wind strength, CO2 and climate are poorly understood and there are very few studies within the core belt of the SHW in the sub-Antarctic zone c.46 to 60 deg South. We have been attempting to address this by producing centennial to decadal reconstructions of changes in SHW strength at sub-Antarctic islands in each of the major sectors of the Southern Ocean. In this talk we will show how lake sediments and peat deposits on the west coasts of these islands can yield proxy-based reconstructions of past changes in the SHW. We will review the statistical performance of our inference models, their application down selected sediment cores, and compare them with complimentary proxies of changes in wind strength based on precipitation and minerogenic inputs. The next phase of the project will use GCM simulations to help understand the patterns seen in the observational data and identify the drivers of past changes in the SHW

A paleolimnological reconstruction of Holocene climate change in southern Patagonia

To fully understand the Holocene climatic variability in the sub-polar latitudes of the Southern Hemisphere and its driving mechanisms, like the Southern Hemisphere westerly winds, we undertook a multi-proxy analysis of a lake sediment core from Lago Pato (51°18.020’S, 72°40.716’W; Chile). The bottom sediments of the core are of glaciogenic origin and gave bulk ages of 30 000 - 22 000 cal. yr. B.P. These are overlain by brown, organic rich sediments which are 9500 cal. yr. B.P. old. The hiatus between both stratigraphic units is possibly related to sediment erosion as a result of the outflow of a large lake after regional deglaciation of the Patagonian Ice Sheet. The pollen record and a diverse benthic diatom community in the Holocene sediments point to dry conditions between ca. 9500 and 6035 cal. yr. B.P. This is coincident with the Early Holocene climate optimum recorded in for example the North Atlantic and Antarctica. From 6035 cal. yr. B.P. until the most recent period a higher biological production compared with the Early Holocene can be inferred from all proxies, probably resulting from wetter and/or warmer conditions. Apart from the diatoms, changes in the proxies are small since the Mid Holocene. The establishment of a planktonic diatom flora between 6035 and 3780 cal. yr. B.P. with the presence of the small diatom Discostella stelligera s.l. as well as the larger species Aulacoseira ambigua, A. granulata s.l. and Cyclostephanos cf. patagonicus possibly points to a period with sufficient mixing during autumn, winter or spring as well as enhanced thermal stratification during summer. Between ca. 3780 and 2080 the diatom community is dominated by Discostella stelligera which suggest a reduced water column mixing and a more stable lake stratification. From ca. 2080 cal. yr. B.P. till present an abrupt shift to and dominance of small chain-forming benthic fragilariod diatoms took place. This period is coincident with the Neoglacial cooling and could be the result of a change in lake-level, longer ice-cover, a turbid/low-nutrient environment, or a more alkaline environment. In the most recent sediments also an increase of Cyclotella cf. meneghiniana could be noticed