Summer-season mesoscale cyclones in the bellingshausen-weddell region of the antarctic and links with the synoptic-scale environment

first_imgResults are presented from the first investigation into a summer-season of mesoscale vortex activity in a large sector of the Antarctic coastal region. The study is based on an analysis of 3 months’ meteorological satellite imagery collected at the British Research Station ‘Rothera’ on the Antarctic Peninsula. The study revealed the high frequency with which such systems occur, with 162 individual vortices being found during the period December 1983 to February 1984 inclusive. The preferred area for their development was in the latitude band 60–70°S over the marginal ice zone and ice-free region of the eastern Bellingshausen Sea. A classification scheme for the vortices was developed based on the relationship with the broad-scale synoptic flow, the sea ice, and the geographical location. The most common type of vortex found was the ‘classic’ polar low, which formed in the southerly flow to the west of synoptic-scale disturbances. These vortices were very similar to the baroclinic type of polar lows observed south of Iceland during the Northern Hemisphere winter. A third of the vortices in total were found to be mesoscale features associated with synoptic-scale troughs or the centres of major depressions. Vortices with comma-shaped cloud signatures occurred about twice as frequently as those with spiraliform cloud. The vast majority of vortices had a diameter of less than 500 km, with very few systems being observed in the range 500–1000 km. Mean anomalies of 500 hPa geopotential height and surface pressure for the occasions when vortices were identified were —5.3 dm and — 0.5 hPa, respectively, indicating the association of these systems with upper air troughs and cold pools. Only 23 of the vortices found were correctly represented on the Meteorological Office analyses and of these 15 were small synoptic disturbances. The ‘polar low’ class of vortex was very poorly represented in the analyses, indicating that the available satellite sounder data could not resolve the systems and that the processes resulting in their formation were not handled well by forecast/data assimilation schemes. Comparison of the mean surface and 500 hPa height fields for this 3-month period with the long-term average data show that there were negative anomalies at both levels over the Bellingshausen Sea. The number of vortices over the Bellingshausen Sea in this summer period may have been greater than would be expected in an average year, but activity over the Weddell Sea was probably close to average.last_img read more

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Biomineralization plasticity and environmental heterogeneity predict geographical resilience patterns of foundation species to future change

first_imgAlthough geographical patterns of species’ sensitivity to environmental changes are defined by interacting multiple stressors, little is known about compensatory processes shaping regional differences in organismal vulnerability. Here, we examine large‐scale spatial variations in biomineralization under heterogeneous environmental gradients of temperature, salinity and food availability across a 30° latitudinal range (3,334 km), to test whether plasticity in calcareous shell production and composition, from juveniles to large adults, mediates geographical patterns of resilience to climate change in critical foundation species, the mussels Mytilus edulis and M. trossulus. We find shell calcification decreased towards high latitude, with mussels producing thinner shells with a higher organic content in polar than temperate regions. Salinity was the best predictor of within‐region differences in mussel shell deposition, mineral and organic composition. In polar, subpolar, and Baltic low‐salinity environments, mussels produced thin shells with a thicker external organic layer (periostracum), and an increased proportion of calcite (prismatic layer, as opposed to aragonite) and organic matrix, providing potentially higher resistance against dissolution in more corrosive waters. Conversely, in temperate, higher salinity regimes, thicker, more calcified shells with a higher aragonite (nacreous layer) proportion were deposited, which suggests enhanced protection under increased predation pressure. Interacting effects of salinity and food availability on mussel shell composition predict the deposition of a thicker periostracum and organic‐enriched prismatic layer under forecasted future environmental conditions, suggesting a capacity for increased protection of high‐latitude populations from ocean acidification. These findings support biomineralization plasticity as a potentially advantageous compensatory mechanism conferring Mytilus species a protective capacity for quantitative and qualitative trade‐offs in shell deposition as a response to regional alterations of abiotic and biotic conditions in future environments. Our work illustrates that compensatory mechanisms, driving plastic responses to the spatial structure of multiple stressors, can define geographical patterns of unanticipated species resilience to global environmental change.last_img read more

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