Antarctic Climate Change Research Articles

Southern Ocean control on the extent of denitrification in the southeast Pacific over the last 70 ka

Temporal changes in oceanic denitrification, the bacterial reduction of nitrate under suboxic conditions, highlight the potential importance of N inventory changes and the production of N 2O on the climate system. At the same time, the cause of the globally observed variation in denitrification remains unclear. High-resolution benthic foraminiferal oxygen isotope and bulk sediment nitrogen isotope records from ODP Site 1234 on the Chile Margin record integrated denitrification changes within the Peru–Chile Upwelling system over the last ∼70 ka. Denitrification changes in the southeast Pacific are coherent with Antarctic climate changes recorded by the Byrd ice core δ 18O record, and lead northern hemisphere climate events. The southern-hemisphere character of the Chile margin δ 15N record suggests that episodes of reduced denitrification in the SE Pacific represent times when more oxygen was supplied as the result of changes in the ventilation and preformed nutrient content of Subantarctic Mode Water (SAMW), which forms in the Subantarctic zone of the Southern Ocean and feeds into the low-latitude thermocline.

A physical mechanism of the atmospheric response over Antarctica to decadal trends in tropical SST

The atmospheric response to the tendency of oceanic equatorial temperature observed during recent decades has been simulated, leading to the identification of a possible link between tropical Sea Surface Temperature (SST) and Antarctic climate change. The dynamical mechanism, by which changes in tropical SSTs exert an influence on the upper latitude atmospheric dynamics, is investigated. The analysis of the simulations suggests that the perturbations of the atmospheric circulation are induced by changes in the annual cycle of the tropical convective activity, which influences the intensity of the wave forcing. In particular, the introduction of the SST perturbation generates a strong vertical wind shear at middle latitude during the Antarctic winter affecting the propagation of convectively generated waves during the following spring.

Soft Law with Hidden Teeth: The Case for a FAO International Plan of Action on Sea Turtles

† B.A., LL.B., Dip.Ed., Ph.D., Law School and Antarctic Climate Change and Ecosystem CRC, University of Tasmania, Australia. Gail.Lugten@utas.edu.au

A synthesis of bentho-pelagic coupling on the Antarctic shelf: Food banks, ecosystem inertia and global climate change

Abstract The Antarctic continental shelf is large, deep (500–1000 m), and characterized by extreme seasonality in sea-ice cover and primary production. Intense seasonality and short pelagic foodwebs on the Antarctic shelf may favor strong bentho-pelagic coupling, whereas unusual water depth combined with complex topography and circulation could cause such coupling to be weak. Here, we address six questions regarding the nature and strength of coupling between benthic and water-column processes on the continental shelf surrounding Antarctica. We find that water-column production is transmitted to the shelf floor in intense pulses of particulate organic matter, although these pulses are often difficult to correlate with local phytoplankton blooms or sea-ice conditions. On regional scales, benthic habitat variability resulting from substrate type, current regime, and iceberg scour often may obscure the imprint of water-column productivity on the seafloor. However, within a single habitat type, i.e. the muddy sediments that characterize much of the deep Antarctic shelf, macrobenthic biomass appears to be correlated with regional primary production and sea-ice duration. Over annual time-scales, many benthic ecological processes were initially expected to vary in phase with the extraordinary boom/bust cycle of production in the water column. However, numerous processes, including sediment respiration, deposit feeding, larval development, and recruitment, often are poorly coupled to the summer bloom season. Several integrative, time-series studies on the Antarctic shelf suggest that this lack of phasing may result in part from the accumulation of a persistent sediment food bank that buffers the benthic ecosystem from the seasonal variability of the water column. As a consequence, a variety of benthic parameters (e.g., sediment respiration, inventories of labile organic matter, macrobenthic biomass) may act as “low-pass” filters, responding to longer-term (e.g., inter-annual) trends in water-column production. Bentho-pelagic coupling clearly will be altered by Antarctic climate change as patterns of sea-ice cover and water-column recycling vary. However, the nature of such climate-driven changes will be very difficult to predict without further studies of Antarctic benthic ecosystem response to (1) inter-annual variability in export flux, and (2) latitudinal gradients in duration of sea-ice cover and benthic ecosystem function.

Simulation of Polar Antarctic trends: Influence of tropical SST

The polar Antarctic atmosphere has been recently characterized by a progressive intensification of the circumpolar westerly winds, both in the stratospheric and tropospheric component. We simulate the response of the polar southern hemisphere atmosphere to a prescribed trend of oceanic equatorial temperature to demonstrate a possible link between the progressive warming of tropical sea surface temperature (SST) and Antarctic climate changes in the last decades. Model simulations produce an atmospheric response suggesting an influence of equatorial SST on polar dynamics, particularly during summer months.

Antarctic climate change during the last 50 years

An erratum has been published for this article in International Journal of Climatology 25 (8) 2005, 1147–1148. The Reference Antarctic Data for Environmental Research (READER) project data set of monthly mean Antarctic near-surface temperature, mean sea-level pressure (MSLP) and wind speed has been used to investigate trends in these quantities over the last 50 years for 19 stations with long records. Eleven of these had warming trends and seven had cooling trends in their annual data (one station had too little data to allow an annual trend to be computed), indicating the spatial complexity of change that has occurred across the Antarctic in recent decades. The Antarctic Peninsula has experienced a major warming over the last 50 years, with temperatures at Faraday/Vernadsky station having increased at a rate of 0.56 °C decade−1 over the year and 1.09 °C decade−1 during the winter; both figures are statistically significant at less than the 5% level. Overlapping 30 year trends of annual mean temperatures indicate that, at all but two of the 10 coastal stations for which trends could be computed back to 1961, the warming trend was greater (or the cooling trend less) during the 1961–90 period compared with 1971–2000. All the continental stations for which MSLP data were available show negative trends in the annual mean pressures over the full length of their records, which we attribute to the trend in recent decades towards the Southern Hemisphere annular mode (SAM) being in its high-index state. Except for Halley, where the trends are constant, the MSLP trends for all stations on the Antarctic continent for 1971–2000 were more negative than for 1961–90. All but two of the coastal stations have recorded increasing mean wind speeds over recent decades, which is also consistent with the change in the nature of the SAM. Copyright © 2005 Royal Meteorological Society

Cenozoic history of Antarctic benthic diatoms

Antarctic Cenozoic climate changes have influenced the development of the Southern Ocean benthic diatom flora. When Antarctica and South America separated in the late Eocene (∼37 Ma), giving rise to the proto-Antarctic Circumpolar Current (ACC), the environment gradually changed from temperate alpine glacial to subpolar with ice sheet development. By the early Oligocene (∼ 30 Ma), at least thirteen new benthic diatom genera had appeared in the Antarctic. Many of the genera probably migrated from lower latitudes (e.g. New Zealand) prior to the ACC becoming fully established (23 ± 2.5 Ma), which increased the physical separation of Antarctica. Further migration may have occurred during later periods of climate warming, but the Cenozoic was generally a time of progressive climate cooling, and increased glaciation that may have caused diatom extinctions. Some genera became extinct during the late Pliocene and Pleistocene, for example, when glaciers covered much of the Antarctic continental shelf. Many of the benthic diatom genera now extinct in Antarctica still occur in ice-free environments at lower latitudes. Most extant benthic Antarctic diatom taxa are eurytopic and probably survived Cenozoic glaciations by either inhabiting sea-ice or becoming planktic, as sea-floor habitats were restricted.

Atmospheric methane during the last four glacial‐interglacial cycles: Rapid changes and their link with Antarctic temperature

Atmospheric methane (CH4) recorded in Antarctic ice cores represents the closest ice proxy available for Greenland temperature changes beyond times when Greenland climate records are available. The record over four climatic cycles from the Vostok ice core offers the opportunity to study the phase relationship between Greenland and Antarctic climate changes through detailed CH4 profiles. Combining American and French analytical efforts, we have improved the time resolution of the existing CH4 record from Petit et al. [1999]. Spectral analyses reveal high‐ and low‐frequency variability (including a strong precessional component). The phase relationship between CH4 and the Antarctic temperature proxy (δD) shows a systematic lag of CH4 versus temperature by 1100 ± 200 years, on long timescales (50–400 kyr) and a more complex behavior over shorter timescales (i.e., ≤25 kyr), suggesting that Dansgaard/Oeschger‐type of climatic variability and associated interhemispheric linkage are robust features of late Quaternary climate.

Variability and Trends of the Summer Melt Period of Antarctic Ice Margins since 1980 from Microwave Sensors

Abstract The density and range of observations made by meteorological stations is insufficient to fully characterize decadal climate variability in Antarctica. Satellite-borne instruments, which offer a high spatial and temporal density of information, can contribute complementary data for characterizing Antarctic climate change. Here, partial melting of Antarctic snow, which significantly affects the microwave emissivity of the surface, is identified and counted over 18 yr in the 20-yr period 1980–99. The cumulated product of the surface area affected by melting and the duration of the melting event, called cumulative melting surface (CMS), is one of the three melt indices defined and discussed here. On average over the last 20 yr, the Antarctic CMS has decreased by 1.8% ± 1% yr−1, a result that is consistent with a mean January cooling of the continent recently identified from infrared satellite data. In addition, the interannual signatures of the Antarctic Oscillation, and possibly of the Southern Osci...

Мониторинг малых ледников как индикаторов изменений климата в районе Антарктического полуострова

Мониторинг малых ледников как индикаторов изменений климата в районе Антарктического полуострова

Asynchrony of Antarctic and Greenland climate change during the last glacial period

A central issue in climate dynamics is to understand how the Northern and Southern hemispheres are coupled during climate events. The strongest of the fast temperature changes observed in Greenland (so-called Dansgaard–Oeschger events) during the last glaciation have an analogue in the temperature record from Antarctica. A comparison of the global atmospheric concentration of methane as recorded in ice cores from Antarctica and Greenland permits a determination of the phase relationship (in leads or lags) of these temperature variations. Greenland warming events around 36 and 45 kyr before present lag their Antarctic counterpart by more than 1 kyr. On average, Antarctic climate change leads that of Greenland by 1–2.5 kyr over the period 47–23 kyr before present.

Local orbital forcing of antarctic climate change during the last interglacial

During the last interglacial, Antarctic climate changed before that of the Northern Hemisphere. Large local changes in precession forcing could have produced this pattern if there were a rectified response in sea ice cover. Results from a coupled sea ice-ocean general circulation model supported this hypothesis when it was tested for three intervals around the last interglacial. Such a mechanism may play an important role in contributing to phase offsets between Northern and Southern Hemisphere climate change for other time intervals.

The sedimentary record of Antarctic climate change

Circum-Antarctic marine sediments contain a record of past climate and Southern Ocean circulation that both complements and considerably extends the record in the continental ice. Variations in primary biological production, reflecting changes in sea-ice cover and sea surface temperature, in bottom current strength and the size of the grounded continental ice sheet, all contribute to changes in sediment characteristics, in a record extending back m any million years. It is possible to assess both the value of the proxy record in Antarctic sediments, and the validity of the analogue approach to understanding climate change, by focusing on the last glacial cycle and, for comparison, on earlier periods that were significantly different: the Pliocene before 3 Ma ago that could provide an analogue for global warming, and the Oligocene before there was an Antarctic Circumpolar Current.