West Antarctic Peninsula: An Ice-Dependent Coastal Marine Ecosystem in Transition
TL;DR: The extent, duration, and seasonality of sea ice and glacial discharge strongly influence Antarctic marine ecosystems as mentioned in this paper, and it is unclear to what extent the ecosystems we observe today differ from the pristine state.
Abstract: The extent, duration, and seasonality of sea ice and glacial discharge strongly influence Antarctic marine ecosystems. Most organisms' life cycles in this region are attuned to ice seasonality. The annual retreat and melting of sea ice in the austral spring stratifies the upper ocean, triggering large phytoplankton blooms. The magnitude of the blooms is proportional to the winter extent of ice cover, which can act as a barrier to wind mixing. Antarctic krill, one of the most abundant metazoan populations on Earth, consume phytoplankton blooms dominated by large diatoms. Krill, in turn, support a large biomass of predators, including penguins, seals, and whales. Human activity has altered even these remote ecosystems. The western Antarctic Peninsula region has warmed by 7°C over the past 50 years, and sea ice duration has declined by almost 100 days since 1978, causing a decrease in phytoplankton productivity in the northern peninsula region. Besides climate change, Antarctic marine systems have been greatly altered by harvesting of the great whales and now krill. It is unclear to what extent the ecosystems we observe today differ from the pristine state.
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01 Dec 2012
TL;DR: In this article, the authors present a data set of satellite-tracked sea-ice motion for the period of 1992-2010 that reveals large and statistically significant trends in Antarctic ice drift, which, in most sectors, can be linked to local winds.
Abstract: The sea-ice cover around Antarctica has experienced a slight expansion in area over the past decades1, 2. This small overall increase is the sum of much larger opposing trends in different sectors that have been proposed to result from changes in atmospheric temperature or wind stress3, 4, 5, precipitation6, 7, ocean temperature8, and atmosphere or ocean feedbacks9, 10. However, climate models have failed to reproduce the overall increase in sea ice11. Here we present a data set of satellite-tracked sea-ice motion for the period of 1992–2010 that reveals large and statistically significant trends in Antarctic ice drift, which, in most sectors, can be linked to local winds. We quantify dynamic and thermodynamic processes in the internal ice pack and show that wind-driven changes in ice advection are the dominant driver of ice-concentration trends around much of West Antarctica, whereas wind-driven thermodynamic changes dominate elsewhere. The ice-drift trends also imply large changes in the surface stress that drives the Antarctic ocean gyres, and in the fluxes of heat and salt responsible for the production of Antarctic bottom and intermediate waters.
425 citations
TL;DR: The State of the Climate for 2016 as discussed by the authors is a very low-resolution file and it can be downloaded in a few minutes for a high-resolution version of the report to download.
Abstract: Editor’s note: For easy download the posted pdf of the State of the Climate for 2016 is a very low-resolution file. A high-resolution copy of the report is available by clicking here. Please be patient as it may take a few minutes for the high-resolution file to download.
253 citations
TL;DR: It is shown that positive anomalies in chlorophyll-a (chl-a) at Palmer Station, occurring every 4-6 years, are constrained by physical processes in the preceding winter/spring and a negative phase of the Southern Annular Mode (SAM).
Abstract: Understanding the mechanisms by which climate variability affects multiple trophic levels in food webs is essential for determining ecosystem responses to climate change. Here we use over two decades of data collected by the Palmer Long Term Ecological Research program (PAL-LTER) to determine how large-scale climate and local physical forcing affect phytoplankton, zooplankton and an apex predator along the West Antarctic Peninsula (WAP). We show that positive anomalies in chlorophyll-a (chl-a) at Palmer Station, occurring every 4-6 years, are constrained by physical processes in the preceding winter/spring and a negative phase of the Southern Annular Mode (SAM). Favorable conditions for phytoplankton included increased winter ice extent and duration, reduced spring/summer winds, and increased water column stability via enhanced salinity-driven density gradients. Years of positive chl-a anomalies are associated with the initiation of a robust krill cohort the following summer, which is evident in Adelie penguin diets, thus demonstrating tight trophic coupling. Projected climate change in this region may have a significant, negative impact on phytoplankton biomass, krill recruitment and upper trophic level predators in this coastal Antarctic ecosystem.
229 citations
TL;DR: In this paper, the authors summarize the research to date on observing these trends, identifying their drivers, and assessing the role of anthropogenic climate change in Antarctic sea ice cover, concluding that the expected response is small compared to the very high natural variability of the system.
203 citations
Cites background from "West Antarctic Peninsula: An Ice-De..."
...…have impacted the distribution of penguin species, with sea ice-obligate Adélie penguins being replaced by ice-tolerant gentoo and chinstrap penguins in the western Antarctic Peninsula where sea ice is in strong decline (McClintock et al., 2008; Massom and Stammerjohn, 2010; Ducklow et al., 2013)....
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01 Jul 2015
TL;DR: Longterm changes and sub-decadal cycles of WAP macrozooplankton community composition may affect energy transfer to higher trophic levels, and alter biogeochemical cycling in this seasonally productive and sensitive polar ecosystem.
Abstract: The Western Antarctic Peninsula (WAP) is one of the most rapidly warming regions on Earth, and where a high apex predator biomass is supported in large part by macrozooplankton. We examined trends in summer (January–February) abundance of major taxa of macrozooplankton along the WAP over two decades (1993–2013) and their relationship with environmental parameters (sea ice, atmospheric climate indices, sea surface temperature, and phytoplankton biomass and productivity). Macrozooplankton were collected from the top 120 m of the water column in a mid-Peninsula study region divided into latitudinal (North, South, and Far South) and cross-shelf (coastal, shelf, slope) sub-regions. Trends for krill species included a 5-year cycle in abundance peaks (positive anomalies) for Euphausia superba, but no directional long-term trend, and an increase in Thysanoessa macrura in the North; variability in both species was strongly influenced by primary production 2-years prior. E. crystallorophias abundance was best explained by the Southern Annular Mode (SAM) and Multivariate El Nino Southern Oscillation Index (MEI), and was more abundant in higher ice conditions. The salp Salpa thompsoni and thecosome pteropod Limacina helicina cycled between negative and positive anomalies in the North, but showed increasing positive anomalies in the South over time. Variation in salp and pteropod abundance was best explained by SAM and the MEI, respectively, and both species were more abundant in lower ice conditions. There was a long-term increase in some carnivorous gelatinous zooplankton (polychaete worm Tomopteris spp.) and amphipods. Abundance of Pseudosagitta spp. chaetognaths was closely related to SAM, with higher abundance tied to lower ice conditions. Longterm changes and sub-decadal cycles of WAP macrozooplankton community composition may affect energy transfer to higher trophic levels, and alter biogeochemical cycling in this seasonally productive and sensitive polar ecosystem.
137 citations
Cites background from "West Antarctic Peninsula: An Ice-De..."
...…Station on Anvers Island is presently nearly ice-free (sea ice season duration 3.5 months), while in the south (Marguerite Bay southward) perennial sea ice still persists ( 7.5 months) – although sea ice has decreased in extent and duration throughout the WAP over time (Ducklow et al., 2013)....
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...A consequence of this regional warming is that a latitudinal climate gradient exists along the length of the WAP, with a warmer, moist, maritime climate in the north, and a colder, drier, continental climate in the south (Smith et al., 1999; Ducklow et al., 2012a, 2012b, 2013)....
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References
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TL;DR: The mean trophic level of the species groups reported in Food and Agricultural Organization global fisheries statistics declined from 1950 to 1994, and results indicate that present exploitation patterns are unsustainable.
Abstract: The mean trophic level of the species groups reported in Food and Agricultural Organization global fisheries statistics declined from 1950 to 1994. This reflects a gradual transition in landings from long-lived, high trophic level, piscivorous bottom fish toward short-lived, low trophic level invertebrates and planktivorous pelagic fish. This effect, also found to be occurring in inland fisheries, is most pronounced in the Northern Hemisphere. Fishing down food webs (that is, at lower trophic levels) leads at first to increasing catches, then to a phase transition associated with stagnating or declining catches. These results indicate that present exploitation patterns are unsustainable.
4,397 citations
TL;DR: This database shows that the productive southwest Atlantic sector contains >50% of Southern Ocean krill stocks, but here their density has declined since the 1970s, and salps appear to have increased in the southern part of their range.
Abstract: Antarctic krill (Euphausia superba) and salps (mainly Salpa thompsoni) are major grazers in the Southern Ocean, and krill support commercial fisheries. Their density distributions have been described in the period 1926-51, while recent localized studies suggest short-term changes. To examine spatial and temporal changes over larger scales, we have combined all available scientific net sampling data from 1926 to 2003. This database shows that the productive southwest Atlantic sector contains >50% of Southern Ocean krill stocks, but here their density has declined since the 1970s. Spatially, within their habitat, summer krill density correlates positively with chlorophyll concentrations. Temporally, within the southwest Atlantic, summer krill densities correlate positively with sea-ice extent the previous winter. Summer food and the extent of winter sea ice are thus key factors in the high krill densities observed in the southwest Atlantic Ocean. Krill need the summer phytoplankton blooms of this sector, where winters of extensive sea ice mean plentiful winter food from ice algae, promoting larval recruitment and replenishing the stock. Salps, by contrast, occupy the extensive lower-productivity regions of the Southern Ocean and tolerate warmer water than krill. As krill densities decreased last century, salps appear to have increased in the southern part of their range. These changes have had profound effects within the Southern Ocean food web.
1,103 citations
TL;DR: In this paper, the authors demonstrate that the adjacent ocean showed profound coincident changes, with surface summer temperatures rising more than 1°C and a strong upper-layer salinification.
Abstract: The climate of the Western Antarctic Peninsula (WAP) is the most rapidly changing in the Southern Hemisphere, with a rise in atmospheric temperature of nearly 3°C since 1951 and associated cryospheric impacts. We demonstrate here, for the first time, that the adjacent ocean showed profound coincident changes, with surface summer temperatures rising more than 1°C and a strong upper-layer salinification. Initially driven by atmospheric warming and reduced rates of sea ice production, these changes constitute positive feedbacks that will contribute significantly to the continued climate change. Marine species in this region have extreme sensitivities to their environment, with population and species removal predicted in response to very small increases in ocean temperature. The WAP region is an important breeding and nursery ground for Antarctic krill, a key species in the Southern Ocean foodweb with a known dependence on the physical environment. The changes observed thus have significant ecological implications.
833 citations
TL;DR: The ozone hole phenomenon was identified and attributed to ozone depletion over Antarctica in a special edition of Nature (http://wwwnaturecom.com/nature/focus/ ozonehole/).
Abstract: Roughly 90% of atmospheric ozone is found in the lower stratosphere in the ozone layer Since about the 1970s, anthropogenic emissions of ozone-depleting gases have led to depletion of ~3–4% of the total overhead ozone averaged over the globe 1 The strongest depletion is found over Antarctica during spring, when photochemical processes combine with a unique set of meteorological conditions to greatly increase the effectiveness of ozone-depleting gases, and more than half of the total overhead ozone is destroyed Characteristics of the resulting Antarctic ozone hole are reviewed in refs 1 and 2, and the identification and attribution of the phenomenon was recently celebrated in a special edition of Nature (http://wwwnaturecom/nature/focus/ ozonehole/) The Antarctic ozone hole is evident in ozone observations taken every spring since about the early 1980s 1 Its annual onset coincides with the return of sunlight to the cold polar stratosphere during September/October, and its decay with the collapse of the stratospheric vortex during November/December 1,2 The most obvious surface impact is an increase in ultraviolet radiation reaching the surface 1 Over the past decade, however, it has become clear that the ozone hole is also associated with widespread changes in the Southern Hemisphere tropospheric circulation and surface climate Our purpose here is to review the evidence that suggests that the Antarctic ozone hole has had a demonstrable effect on the surface climate of the Southern Hemisphere The ozone hole and Southern Hemisphere circulation Ozone absorbs incoming solar radiation Hence the depletion of ozone over Antarctica leads to cooling of the polar stratosphere 2,3
820 citations
TL;DR: The continued retreat of ice shelves on the Antarctic Peninsula has been widely attributed to recent atmospheric warming, but there has been little published work describing changes in glacier margin positions as discussed by the authors, which suggests that this may not be the sole driver of glacier retreat in this region.
Abstract: The continued retreat of ice shelves on the Antarctic Peninsula has been widely attributed to recent atmospheric warming, but there is little published work describing changes in glacier margin positions. We present trends in 244 marine glacier fronts on the peninsula and associated islands over the past 61 years. Of these glaciers, 87% have retreated and a clear boundary between mean advance and retreat has migrated progressively southward. The pattern is broadly compatible with retreat driven by atmospheric warming, but the rapidity of the migration suggests that this may not be the sole driver of glacier retreat in this region.
806 citations