Time filter

Source Type

Kiko R.,Institute for Polar Ecology | Kiko R.,Alfred Wegener Institute for Polar and Marine Research | Kiko R.,Leibniz Institute of Marine Science
Polar Biology | Year: 2010

Sea ice is permeated by small brine channels, which are characterised by sub-zero temperatures and varying salinities. Despite sometimes extreme conditions a diverse fauna and flora thrives within the brine channels. The dominant calanoid copepods of Antarctic sea ice are Stephos longipes and Paralabidocera antarctica. Here, I report for the first time thermal hysteresis (TH) in the haemolymph of a crustacean, S. longipes, whereas P. antarctica has no such activity. TH, the non-colligative prevention of ice growth, seems to enable S. longipes to exploit all available microhabitats within sea ice, especially the surface layer, in which strong temperature fluctuations can occur. In contrast, P. antarctica only thrives within the lowermost centimetres of sea ice, where temperature fluctuations are moderate. S. longipes possesses two isoforms of a protein with TH activity. A high homology to a group of (putative) antifreeze proteins from diatoms, bacteria and a snow mold and, in contrast, no homologs in any metazoan lineage suggest that this protein was obtained through horizontal gene transfer (HGT). Further analysis of available sequence data from sea-ice organisms indicates that these antifreeze proteins were probably transferred horizontally several times. Temperature and salinity fluctuations within the brine channel system are proposed to provide "natural transformation" conditions enabling HGT and thus making this habitat a potential "hot spot" for HGT. © 2009 Springer-Verlag.

A primitive linear model is applied to quantify potential salt rejection and theoretical salinity increase in the standardized water column of 46 individual circum-Arctic flaw leads/polynyas based on intermediate salinities, seasonal ice production rates, and flaw lead/polynya size. Analysis shows that open water with low initial salinity may not reject enough salt to produce enhanced salinities despite high ice formation rates. Conversely, flaw leads/polynyas with higher initial salinities in combination with moderate to high ice formation rates produce sufficient salt to increase flaw lead/polynya salinities. Flaw leads/polynyas with maximum potential for theoretical salinity increase and dense brine formation are located along the Beaufort Sea coast, where both initial salinities and ice formation rates are high. Salinity increase is generally moderate to high in Chukchi Sea flaw leads/polynyas, and widely moderate in the East Siberian, Kara, and Barents Seas. Southern central and southeastern Laptev Sea flaw leads/polynyas show weak potentials for salt rejection, theoretical salinity increase and dense brine formation due to extremely low salinities and ice formation rates. Though the formation of dense brines on Arctic shelves is a complex process in nature, the simplified model provides a suitable and quick (graphic) tool for Arctic marine geologists and biologists or cold region engineers to compare individual flaw lead/polynya sections in terms of freeze-related potential salt rejection and theoretical salinity increase. © 2010 Elsevier B.V.

Dethleff D.,Institute for Polar Ecology
Journal of Geophysical Research: Oceans | Year: 2010

Two primitive equation-based models are used to estimate the formation of total volumes either of Arctic cold halocline water (CHW), intermediate water (IMW), or deep water (DW) through freeze-related salt rejection in the Siberian Laptev Sea flaw lead system. Model A assumes that the rejected salt remixes with surface mixed water (SMW) beyond the leads until salinities allow for contribution to the midlayers of either the CHW, the IMW, or the DW. Model B simulates direct salt rejection to the upper layer of the cold halocline, and, after remixing here, further contribution to the midlayers of CHW, IMW, or DW. Averaging both model estimates, Laptev leads contribute either 0.161 Sv of CHW, 0.075 Sv of IMW, or 0.065 Sv of DW, which represents as much as ∼23%, ∼16%, or ∼30% of Arctic-wide lead derived dense water contribution to the appropriate layer, respectively. Northwestern Laptev leads produce the greatest amount of dense water. These lead sections show very short buoyancy equilibrium timescales (∼6 to ∼13 days), and local dense water production may potentially be amplified by lateral brine injection into the cold halocline through bottom eddies. Central-southern and southeastern leads generally produce little salt due to low surface water salinities. As definite separation mechanisms and proportion distributions of rejected lead brines into CHW, IWM, and DW are still unidentified in nature, a combination of lead salt rejection and remixing (model A) and direct downward expulsion of brine packages (model B) is assumed to steer Laptev lead dense water production. Copyright 2010 by the American Geophysical Union.

Holzinger A.,Institute of Botany | di Piazza L.,Institute of Botany | Lutz C.,Institute of Botany | Roleda M.Y.,Institute for Polar Ecology | Roleda M.Y.,University of Otago
Phycological Research | Year: 2011

Fertile Saccharina latissima sporophytes, collected in the Kongsfjorden, Ny-Ålesund, Spitsbergen, Norway (78°56.87' N, 11°51.64' E) were investigated in relation to its sensitivity to experimentally enhanced ultraviolet radiation:photosynthetically active radiation (UVR:PAR) ratios. Irradiance of UVR were 4.30W m -2 of UV-A (320-400nm) and 0.40W m -2 of UV-B (280-320nm), and PAR (400-700nm) was ~4.30W m -2 (=20μmol photons m -2s -1). Excised soral (sporogenic) and non-soral (vegetative) tissues were separately irradiated for 16h at 7°C. Transmission electron microscopy showed abundant occurrence of physodes, electron dense particles (~300-600nm) in the sorus. Paraphysis cells, with partly crystalline content, large mitochondria and abundant golgi bodies were towering over the sporangia. In soral tissue, cells were not visibly altered by the PAR+UVR irradiation. The chloroplasts, flagella and nucleus of unreleased meiospores inside the sporangial parent cells were visibly intact. Severe changes in the chloroplast structure of vegetative tissue occurred after PAR+UVR irradiation. These changes included wrinkling and dilatation of the thylakoid membranes, and appearance of electron translucent areas inside the chloroplasts. In vegetative cells exposed to PAR+UVR, the total amount of physodes, was slightly higher as in cells exposed to PAR only. Initial values of optimum quantum yield of photosystem II (F v/F m) were 0.743±0.04 in non-soral and 0.633±0.04 in soral tissue. Vegetative tissue was observed to be more sensitive to radiant exposure of PAR and PAR+UVR compared to reproductive tissue. Under PAR, a 20% reduction in Fv/Fm was observed in non-soral compared to no reduction in soral tissue, whereas under PAR+UVR, 60% and 33% reduction in Fv/Fm was observed in non-soral and soral tissues, respectively. This can be attributed to the corresponding three times higher antiradical power (ARP) capacity in soral compared to non-soral tissue. © 2011 Japanese Society of Phycology.

Schulz M.,Leibniz Institute for Baltic Sea Research | Bergmann M.,Alfred Wegener Institute for Polar and Marine Research | von Juterzenka K.,Institute for Polar Ecology | Soltwedel T.,Alfred Wegener Institute for Polar and Marine Research
Polar Biology | Year: 2010

The colonisation of hard substrata (HS) by epibenthic megafauna was studied by photographic surveys along the Ardencaple Canyon in the deep western Greenland Sea in 2000. Seven transects at 2,700-3,200 m water depth showed generally low densities of dropstones, sunken wood, and other substrata including anthropogenic material (range: 2-11 HS km-1). Overall, 30 different taxa and morphotypes were found on or associated with HS. While the sea anemone Bathyphellia margaritacea and the pantopod Ascorhynchus abyssi dominated the fauna on the substrate surfaces, a ball-shaped morphotype of uncertain taxonomic origin characterised assemblages marginally associated with HS. Community analysis revealed differences in faunal patterns near the continental rise and towards the deep sea, but diversity and evenness did not differ significantly between the various regions. However, we conclude that dropstones and other hard substrata at the seafloor serve as colonisation islands and thereby generally increase small-scale habitat diversity in polar deep-sea environments. © 2010 The Author(s).

Discover hidden collaborations