Annual Sea Ice Research Articles

Microbial loop malfunctioning in the annual sea ice at Terra Nova Bay (Antarctica)

We investigated organic carbon quantity and biochemical composition, prokaryotic abundance, biomass and carbon production in the annual and platelet sea ice of Terra Nova Bay (Antarctica), as well as the downward fluxes of organic matter released by melting ice during early spring. Huge amounts of biopolymeric C accumulated in the bottom layer of the ice column concomitantly with the early spring increase in sympagic algal biomass. Such organic material, mostly accounted for by autotrophic biomass, was characterised by a high food quality and was rapidly exported to the sea bottom during sea ice melting. Prokaryote abundance (up to 1.3 × 109 cells L−1) and extracellular enzymatic activities (up to 24.3 μM h−1 for amino-peptidase activity) were extremely high, indicating high rates of organic C degradation in the bottom sea ice. Despite this, prokaryote C production values were very low (range 5–30 ng C L−1 h−1), suggesting that most of the degraded organic C was not channelled into prokaryote biomass. In the platelet ice, we found similar organic C concentrations, prokaryote abundance and biomass values and even higher extracellular enzymatic activities, but values of prokaryote C production (range 800–4,200 ng C L−1 h−1) were up to three orders of magnitude higher than in the intact bottom sea ice. Additional field and laboratory experiments revealed that the dissolved organic material derived from algae accumulating in the bottom sea ice significantly reduced prokaryote C production, suggesting the presence of a potential allopathic control of sympagic algae on prokaryote growth.

Vitamin B12 and cobalt cycling among diatoms and bacteria in Antarctic sea ice microbial communities

Within McMurdo SoundÂs annual sea ice, assimilation and concentrations of vitamin B12 (cobalamin), microbial community productivity, and biomass were examined among three 100‐m2 quadrats where light penetration was manipulated by snow cover during austral summer. From late October through December, B12 concentrations (6−32 pmol L−1) and assimilation rates (17−780 pmol m−2 d−1) in congelation ice covaried with primary productivity (0.0001−250 mmol C m−2 d−1) and chlorophyll a (0.6−36 mg m−2). Within ice core samples, incorporation of 57Co‐B12 into the >1.0‐mm size fraction (mostly diatoms) was almost 100 times faster than into 0.2−1.0−mm particles (mostly heterotrophic bacteria) and was dependent on light and active transport across cell membranes. Microalgal B12:C cell quotas in field communities varied widely (2.6‐150,000 nmol B12 (mol C)−1; x̄x = 500) and generally exceeded those of cultured temperate diatoms (0.4‐55 nmol B12 (mol C)−1; x̄x = 4.1). Comparisons of dissolved B12 pools in the ice and their turnover (0.02‐0.6 d‐1) with underlying seawater suggest that this vitamin is produced in situ rather than delivered from waters below. Production and uptake of B12 and uptake of cobalt, required for B12 synthesis, were then examined among bacteria isolated from these communities. Only 23% of 78 bacterial isolates were incapable of B12 uptake, but these clones assimilated dissolved cobalt. Intracellular B12 production was evident in 9 of the 11 isolates screened and their cell quotas varied widely, 0.6‐6,800 nmol B12 (mol C)‐1. Mass balance analyses and published kinetics data independently suggest that microalgal growth in sea ice was not limited by vitamin B12 in most of our field observations and that in situ bacterial B12 production could potentially meet microalgal demands. Similar analyses, however, suggest that cobalt supply from underlying waters may have limited community growth and B12 production.

Changing sea ice melt parameters in the Canadian Arctic Archipelago: Implications for the future presence of multiyear ice

Estimates of annual sea ice melt onset, freeze onset, and melt duration are made within the Canadian Arctic Archipelago (CAA) using SeaWinds/QuikSCAT data from 2000 to 2007. The average date of melt onset occurred on day 150, the average freeze onset occurred on day 266, and the average number of days of melt was 116. Melt onset occurred first, and freeze onset occurred last within the Amundsen, Western Arctic Waterway, and Eastern Parry Channel regions, whereas the reverse occurred in the Queen Elizabeth Islands (QEI) and the M'Clure and Viscount‐Melville regions. Multiyear sea ice (MYI) increases occurred from 2000 to 2004 because of dynamic import and first‐year sea ice (FYI) being promoted to MYI, but this replenishment virtually stopped from 2005 to 2007, coincident with longer melt seasons. Only after two consecutive long melt seasons (2005–2006) and almost no replenishment were regions to the south of the QEI cleared of MYI. We argue that this is because MYI must slowly ablate on the underside while in transit within the CAA from the small oceanic heat flux and can therefore survive for several years in southern regions without replenishment. Net positive dynamic MYI import into the CAA was observed in 2007 following MYI removal during 2005–2006. Longer melt seasons will continue to reduce the inventory of FYI in the CAA following the melt season. Longer melt seasons within the CAA will likely not reduce MYI dynamic import, but it remains to be seen whether or not this MYI will be able to survive longer melt seasons as it migrates to the southern regions.

Impact of the B-15 iceberg “stranding event” on the physical and biological properties of sea ice in McMurdo Sound, Ross Sea, Antarctica

AbstractIce cores were sampled at four stations in McMurdo Sound (Ross Sea) between 1999 and 2003. At the beginning of year 2000, a very large iceberg (B-15) detached itself from the Ross Ice Shelf and stranded at the entrance of the Sound, preventing the usual oceanic circulation purging of the annual sea ice cover from this area. Ice textural studies showed that a second year sea ice cover was built-up at three out of the four stations: ice thickness increased to about 3 m. Repeated alternation of columnar and platelet ice appeared, and bulk salinity showed a strong decrease, principally in the upper part of the ice sheet, with associated brine volume decrease. Physical modification influenced the biology as well. By decreasing the light and space available for organisms in the sea ice cover, the stranding of B-15 has i) hampered autotrophic productivity, with chlorophyllaconcentration and algae biomass significantly lower for second year ice stations, and ii) affected trophic relationships such as the bacterial biomass/chlaconcentration correlation, or the autotrophic to heterotrophic ratio.

High-resolution trends of nutrients, DOM and nitrogen uptake in the annual sea ice at Terra Nova Bay, Ross Sea

AbstractHigh-resolution trends of nutrients and DOM are analysed, with respect to nitrate and ammonium uptakes, in two coastal stations placed on the annual land-fast ice at Terra Nova Bay. The highest accumulations of dissolved inorganic nitrogen (87.2 µmol N dm-3), reactive phosphorus (14.1 µmol P dm-3) and reactive silicon (22.9 µmol Si dm-3) were observed in the bottom ice, although this process was preceded by a nutrient decrease in an interior sea ice layer. In the upper layer of sea ice, DOM was rather constant in concentration and P-deficient (C:N:P = 377:34:1–579:53:1). In the bottom and platelet ice, the accumulation of DOM (1277 µmol C dm-3; 108.2 µmol N dm-3; 7.67 µmol P dm-3) occurred with lower C:N:P ratios (123:14:1–59:7:1), because of a major contribution of fresher organic matter. Nitrate (< 7.33 µmol N dm-3 d-1) and ammonium (< 2.85 µmol N dm-3 d-1) uptakes in the bottom ice were higher than in the platelet ice. The comparison between the data of N-uptake and the concomitant release of total dissolved nitrogen in the bottom ice indicated that the microbial community may be subjected to low growths in situ and high releases of dissolved nitrogen, when it accumulates in this sea ice habitat.

Trends in Antarctic annual sea ice retreat and advance and their relation to El Niño–Southern Oscillation and Southern Annular Mode variability

Previous studies have shown strong contrasting trends in annual sea ice duration and in monthly sea ice concentration in two regions of the Southern Ocean: decreases in the western Antarctic Peninsula/southern Bellingshausen Sea (wAP/sBS) region and increases in the western Ross Sea (wRS) region. To better understand the evolution of these regional sea ice trends, we utilize the full temporal (quasi‐daily) resolution of satellite‐derived sea ice data to track spatially the annual ice edge advance and retreat from 1979 to 2004. These newly analyzed data reveal that sea ice is retreating 31 ± 10 days earlier and advancing 54 ± 9 days later in the wAP/sBS region (i.e., total change over 1979–2004), whereas in the wRS region, sea ice is retreating 29 ± 6 days later and advancing 31 ± 6 days earlier. Changes in the wAP/sBS and wRS regions, particularly as observed during sea ice advance, occurred in association with decadal changes in the mean state of the Southern Annular Mode (SAM; negative in the 1980s and positive in the 1990s) and the high‐latitude response to El Niño–Southern Oscillation (ENSO). In general, the high‐latitude ice‐atmosphere response to ENSO was strongest when ‐SAM was coincident with El Niño and when +SAM was coincident with La Niña, particularly in the wAP/sBS region. In total, there were 7 of 11 ‐SAMs between 1980 and 1990 and the 7 of 10 +SAMs between 1991 and 2000 that were associated with consistent decadal sea ice changes in the wAP/sBS and wRS regions, respectively. Elsewhere, ENSO/SAM‐related sea ice changes were not as consistent over time (e.g., western Weddell, Amundsen, and eastern Ross Sea region), or variability in general was high (e.g., central/eastern Weddell and along East Antarctica).

The cryopelagic meroplankton community in the shallow waters of Gerlache Inlet, Terra Nova Bay, Antarctica

AbstractLimited sampling has so far been conducted of the meroplankton community of the high Antarctic, with most research being conducted using vertical hauls in waters > 50 m, and little focused research on the meroplankton community directly under the sea ice (cryopelagic). Here we report the composition of the early summer cryopelagic meroplankton community of the shallow waters of Gerlache Inlet, Terra Nova Bay. A fixed-frame stationary plankton net was deployed c. 1 m below the annual sea ice and sampled at c. 24 hour intervals over a period of 19 days from mid-November to early December 2006. A total of 173 larvae from the phyla Annelida (n = 66), Mollusca (n = 30), Nemertea (n = 4), Echinodermata (n = 8), several Pleuragramma antarcticum (n = 4) and numerous planulae (n = 61) were collected, as well as 265 egg/embryo stages. A mean of 9.1 larvae (SD = 7.3, n = 19) and 13.9 eggs/embryos (SD = 20.5, n = 19) were found directly below the sea ice in each 24 hour period, and these early life history stages may be subject to the hazards of extensive platelet ice and penetrating ultraviolet radiation. The cryopelagic meroplankton community of shallow water is also compositionally similar to that of deeper waters, suggesting that the 50–0 m plankton tows used in previous research are providing a reliable assessment of the biodiversity of coastal Antarctic meroplankton.

Role of the bowhead whale as a predator in West Greenland

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 346:285-297 (2007) - DOI: https://doi.org/10.3354/meps06995 Role of the bowhead whale as a predator in West Greenland Kristin L. Laidre1,3,* Mads Peter Heide-Jørgensen1, Torkel Gissel Nielsen2 1Greenland Institute of Natural Resources, Box 570, 3900 Nuuk, Greenland 2National Environmental Research Institute, Department of Marine Ecology, Frederiksborgvej 399, PO Box 358, 4000 Roskilde, Denmark 3Present address: Polar Science Center, Applied Physics Laboratory, University of Washington, 1013 NE 40th Street, Seattle, Washington 98105, USA *Email: klaidre@apl.washington.edu ABSTRACT: We examined the spatial and temporal linkage between primary production, zooplankton distribution and density, and bowhead whale Balaena mysticetus foraging behavior in Disko Bay, West Greenland using concurrent ship-based oceanographic and net sampling together with instrumentation of whales with satellite-linked transmitters and dive recorders. Estimates of bowhead whale abundance were used in a bioenergetic model to calculate the potential consumption of zooplankton during their 4 mo stay in Disko Bay. Between 2001 and 2006, 30 whales were fitted with satellite transmitters that provided information on daily movements, and 14 whales were tracked with archival time–depth or time–depth–fluorescence recorders that provided detailed dive data. Simultaneous data were collected on water column structure, phytoplankton and zooplankton density, taxa and biomass at 25 stations south of Disko Island in 2003, 2005 and 2006. After the retreat of annual winter sea ice, bowhead whales explored a limited area along the south coast of Disko Island and had high interannual site fidelity. Mean dive depths varied between 53 (SD = 35) and 109 (SD = 41) m but maximum dive depths were >400 m. Most dives targeted the bottom and dive durations >40 min were observed for several whales. Available prey for bowhead whales was dominated by calanoid copepods, with Calanus finmarchicus, C. glacialis and C. hyperboreus occurring at 90 to 100% of all stations between 0 and 50 m and contributing 78 ± 25% of the total biomass. Bottom sampling for epizooplankton in 2006 resulted in unprecedented densities of C. finmarchicus, several orders of magnitude higher than at any other depth. Bioenergetic modeling indicated the population consumes ~220 US t of zooplankton per day or >21000 t during the 4 mo stay in Disko Bay. Although the total biomass of zooplankton in the upper 50 m of the water column theoretically could support this predation level, benthic zooplankton densities and behavioral data suggest whales target preascension stage epibenthic copepods in high density patches. KEY WORDS: Bowhead whale · Foraging · Zooplankton · Calanus · Greenland Full text in pdf format PreviousNextCite this article as: Laidre KL, Peter Heide-Jørgensen M, Gissel Nielsen T (2007) Role of the bowhead whale as a predator in West Greenland. Mar Ecol Prog Ser 346:285-297. https://doi.org/10.3354/meps06995 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 346. Online publication date: September 27, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Observations of a wild polar bear (Ursus maritimus) successfully fishing Arctic charr (Salvelinus alpinus) and Fourhorn sculpin (Myoxocephalus quadricornis)

Polar bears, Ursus maritimus, throughout their range, are nutritionally dependent on ringed (Phoca hispida) and bearded seals (Erignathus barbatus), which are predominantly caught on the sea ice. Other marine prey species are caught and consumed, but less frequently. As the annual sea ice retreats, polar bears throughout their range are forced ashore, where they mostly live off their stored adipose tissue. However, while land-bound they have been observed catching birds and terrestrial mammals. Although polar bears evolved from brown bears (U. arctos), direct observations of polar bears diving for and catching fish have not been reported. Here, we document observations of a young male polar bear catching Arctic charr (Salvelinus alpinus) and Fourhorn sculpin (Myoxocephalus quadricornis) by diving in Creswell Bay, Nunavut. We recorded six search bouts, where six fish were caught during dives, which were preceded by a snorkel. The average dive and snorkel length was (mean ± SD) 13 ± 5 and 6 ± 2 s, respectively.

Interannual variation in air‐sea CO2 flux in the Ross Sea, Antarctica: A model analysis

Phytoplankton dynamics, primary production, and air‐sea CO2 exchange in the Ross Sea over a 6‐year period (1997–2003) were investigated using a combination of satellite remote sensing and numerical ecosystem modeling. Sea ice cover in the Ross Sea was highly variable during this time, with 3 years exhibiting a normal springtime retreat of the annual sea ice and 3 years exhibiting very heavy ice cover, particularly 2002–2003. Annual net primary production (NPP) during normal ice years ranged from 141 to 180 g C m−2 yr−1, dropping to 27.3–96.2 g C m−2 yr−1 during heavy ice years. The prymnesiophyte Phaeocystis antarctica was the phytoplankton taxa responsible for the bulk of the annual NPP, although diatoms increased in relative importance during heavy ice years. Reductions in surface water pCO2 due to phytoplankton CO2 fixation during spring and summer and the return of the annual sea ice in the autumn and winter (thus restricting gas exchange) made the Ross Sea a net sink for atmospheric CO2. The magnitude of the annual net flux of CO2 (FCO2) into the Ross Sea varied >twentyfold between years, from −0.07 mol C m−2 in 2002–2003 to −1.55 mol C m−2 in 1999–2000 (negative values denote flux from air to sea). In some regions, annual FCO2 was as high as −2.9 mol C m−2, with daily rates approaching −62 mmol m−2 d−1. These results rank the Ross Sea as one of the stronger ocean sinks for atmospheric CO2 and demonstrate the sensitivity of FCO2 in polar waters to changes in sea ice cover.

Light environment and seasonal dynamics of microalgae in the annual sea ice at Terra Nova Bay, Ross Sea, Antarctica

We investigated the physical conditions of the Spring pack ice environment at Terra Nova Bay to understand their influence on the structure and physiology of sympagic microalgae. Bio-optical methods were used to study the availability and spectral quality of solar radiation, both inside and underneath the ice cover. Pack ice thickness was around 2.5 m, with a temperature between −2 and −7°C. On average, only 1.4% of surface PAR penetrated to the bottom ice and less than 0.6% below platelet ice level. Surface UV-B radiation under the bottom ice was 0.2–0.4%. Biomass concentrations up to 2400 mg Chl a m−3, dominated by two species of diatoms (Entomoneis kjellmannii and Nitschia cf. stellata), showed marked spatial and temporal patterns. Maximum values were in the platelet ice during the first half of November, and in the bottom ice two weeks later. Strong shade adaptation characteristics emerged clearly and explained the relevant abundance of microalgae within the sea ice, with specific absorption coefficients (a*) as low as 0.005 m2 (mg Chl a)−1 and the photo-acclimation index (Ek) in the range of in situ irradiance. The biomass specific production values were low, around 0.12–0.13 mg C mg Chl a−1 h−1. The hypothesis suggesting bottom ice colonization by platelet ice microalgae is supported here.

A diverse benthic assemblage 100 km from open water under the Amery Ice Shelf, Antarctica

A hot water drill was used to penetrate 480 m of ice to reveal a diverse benthic assemblage, dominated by suspension‐feeding invertebrates, under the Amery Ice Shelf (East Antarctica) at a location 100 km from open water and at a depth of 775 m below sea level (840 m below the ice shelf surface). This is the first record of a benthic assemblage of this type found at this distance under an ice shelf. The few previous reports of life under ice shelves describe assemblages with very different trophic strategies (e.g., sparse assemblages of mobile scavengers or chemotrophs) or are in circumstances in which in situ photosynthesis at tide cracks or through the ice cannot be ruled out as a potential source of primary production. The physical characteristics of the Amery Ice Shelf and the feeding strategies represented together indicate that the only likely source of primary production to sustain the benthic assemblage is material advected from open water. This suggestion is supported by observed current speeds in the vicinity and reported rates of particle settling. The observation under an ice shelf of a benthic assemblage that is very similar to those found elsewhere in Antarctica, in locations dominated by annual sea ice or at depths below the photic zone, has implications for the interpretation of sediment paleorecords to represent the history of ice shelf advance and retreat. Without observations of this living assemblage in situ, the remnants of its component species in the sediment record, such as sponge spicules, echinoderm ossicles, and bryozoan fragments, could be interpreted reasonably, but erroneously, to represent open water conditions.

Copepods in spring annual sea ice at Terra Nova Bay (Ross Sea, Antarctica)

The aim of this study was to investigate patterns of abundance, distribution, temporal changes and species composition of the dominant ice-associated copepods in the spring annual pack ice, platelet ice and water column at Terra Nova Bay, Ross Sea, during late spring 1997. Ice cores were drilled for temporal and spatial scales. Stephos longipes and Harpacticus furcifer dominated the sea ice meiofauna in terms of numbers in the lower few centimeters of the bottom ice associated with high chlorophyll a and phaeopigment levels. Nauplii dominated the S. longipes population (91.6%) and occurred in extremely high concentrations. In contrast, copepodids were the dominant stages in H. furcifer. How H. furcifer carries out its entire life cycle and how it differs from ecologically similar species such as Drescheriella glacialis should be examined in more detail.

Baltic Sea climate in the late twenty-first century: a dynamical downscaling approach using two global models and two emission scenarios

A regional ocean circulation model was used to project Baltic Sea climate at the end of the twenty-first century. A set of four scenario simulations was performed utilizing two global models and two forcing scenarios. To reduce model biases and to spin up future salinity the so-called Δ-change approach was applied. Using a regional coupled atmosphere–ocean model 30-year climatological monthly mean changes of atmospheric surface data and river discharge into the Baltic Sea were calculated from previously conducted time slice experiments. These changes were added to reconstructed atmospheric surface fields and runoff for the period 1903–1998. The total freshwater supply (runoff and net precipitation) is projected to increase between 0 and 21%. Due to increased westerlies in winter the annual mean wind speed will be between 2 and 13% larger compared to present climate. Both changes will cause a reduction of the average salinity of the Baltic Sea between 8 and 50%. Although salinity in the entire Baltic might be significantly lower at the end of the twenty-first century, deep water ventilation will very likely only slightly change. The largest change is projected for the secondary maximum of sea water age within the halocline. Further, the average temperature will increase between 1.9 and 3.2°C. The temperature response to atmospheric changes lags several months. Future annual maximum sea ice extent will decrease between 46 and 77% in accordance to earlier studies. However, in contrast to earlier results in the warmest scenario simulation one ice-free winter out of 96 seasons was found. Although wind speed changes are uniform, extreme sea levels may increase more than the mean sea level. In two out of four projections significant changes of 100-year surge heights were found.

Sea ice evolution over the 20th and 21st centuries as simulated by current AOGCMs

Outputs from simulations performed with current atmosphere-ocean general circulation models for the Fourth Assessment Report of Intergovernmental Panel on Climate Change (IPCC AR4) are used to investigate the evolution of sea ice over the 20th and 21st centuries. We first use the results from the “Climate of the 20th Century Experiment” to assess the ability of these models to reproduce the observed sea ice cover changes over the periods 1981–2000 and 1951–2000. The projected sea ice changes over the 21st century in response to the IPCC Special Report on Emission Scenarios A1B are then examined. Overall, there is a large uncertainty in simulating the present-day sea ice coverage and thickness and in predicting sea ice changes in both hemispheres. Over the period 1981–2000, we find that the multimodel average sea ice extent agrees reasonably well with observations in both hemipsheres despite the wide differences between the models. The largest uncertainties appear in the Southern Hemisphere. The climate change projections over the 21st century reveal that the annual mean sea ice extent decreases at similar rates in both hemispheres, and that the reduction in annual mean sea ice volume is about twice that of sea ice extent reduction in the Northern Hemisphere, in agreement with earlier studies. We show that the amplitude of the seasonal cycle of sea ice extent increases in both hemispheres in a warming climate, with a larger magnitude in the Northern Hemisphere. Furthermore, it appears that the seasonal cycle of ice extent is more affected than the one of ice volume. By the end of the 21st century, half of the model population displays an ice-free Arctic Ocean in late summer.

Trace metals distributions in coastal sea ice of Terra Nova Bay, Ross Sea, Antarctica

In an attempt to clarify the release of trace elements from the seasonal coastal sea ice, samples were periodically collected in a nearshore station inside the Gerlache Inlet (Terra Nova Bay, Western Ross Sea), during the summer 2000/01 and analysed for dissolved and particulate cadmium, copper, iron, manganese and lead, as well as salinity, suspended particulate matter, nutrients and phytoplankton pigments. In order to provide insight on the metal association with the particles included in the sea ice, the metal solid speciation was also investigated. Both vertical distributions within the ice cores and temporal variations at the seawater interface were studied, in an effort to fully characterize the system and correlation among the considered parameters. Concentrations and speciation patterns clearly indicate metal incorporation within the annual sea ice due to resuspension of sediments, followed by release of particulate metals during melting as a primary process affecting trace metal availability in the Antarctic coastal waters.

Atmospheric Concentrations and Air−Water Flux of Organochlorine Pesticides along the Western Antarctic Peninsula

Air, seawater, sea ice, and snow were collected during the austral winter (September-October 2001) and summer (January-February 2002) along the Western Antarctic Peninsula. Hexachlorobenzene (HCB) > heptachlor > alpha- and gamma-hexachlorocyclohexane (HCH) and heptachlor epoxide, were the most frequently detected organochlorine pesticides in air. HCB and HCH levels declined over the past 20 years, with a half-life of 3 years for sigmaHCH in Antarctic air. However, heptachlor epoxide levels have not declined in Antarctic air over the past decade, possibly due to continued use of heptachlor in the southern hemisphere. Peak heptachlor concentrations in air were measured coincident with air masses moving into the region from lower latitudes. Levels of lindane were 1.2-200 times higher in annual sea ice and snow compared to alpha-HCH, likely due to greater atmospheric input of gamma-HCH. The ratio of alpha/gamma-HCH in Antarctic air, sea ice and snow was <1, illustrative of a predominance of influx of lindane versus technical HCH to the regional environment. However, alpha/gamma-HCH in seawater was >1, likely due to more rapid microbial degradation of gamma- versus alpha-HCH. Water/air fugacity ratios for HCHs demonstrate continued atmospheric influx of HCHs to coastal Antarctic seas, particularly during late summer.

Transmission of ultraviolet radiation through the Antarctic annual sea ice and its biological effects on sea urchin embryos

Stratospheric ozone depletion over Antarctica is expected to continue for the next 50 years, with increases in ecologically damaging ultraviolet radiation (UVR: 290–400 nm), specifically the ultraviolet‐B (UVB: 290–320 nm) portion of the spectrum. Most of coastal Antarctica is covered with 2–3 m of annual sea ice during the occurrence of the “ozone hole.” This physical barrier to UVR transmission has long been assumed to provide complete protection from the biologically damaging effects of UVR, especially for the planktonic developmental stages of the benthic invertebrate fauna. We found that short‐wavelength UVB (down to 304 nm) is transmitted through the Austral spring annual ice of McMurdo Sound, and causes significant mortality and DNA damage in the embryos of the sea urchin Sterechinus neumayeri. Although mortality of sea urchin embryos has been reported for the open waters of the Antarctic, this is the first documentation of mortality and DNA damage for embryos under the annual sea ice. The degree of mortality and DNA damage was dependent on both year and depth, with higher mortality and DNA damage at 1 m depth below the ice compared to 3 m and 5 m. Greater DNA damage occurred in 2003 compared to 2002 despite the thicker annual ice (3.1 m vs. 2.5 m). Although the thickness of the annual ice was greater, the severity of the ozone hole, 230 Dobson units (DU) versus 320 DU, and the ratio of UVB to visible radiation was greater in 2003. Embryo and larval mortality from exposure to UVR under the annual ice should be considered as another abiotic factor potentially affecting the temporally episodic recruitment of invertebrates that occur in this benthic ecosystem.

Accounts from 19th‐century Canadian Arctic explorers' logs reflect present climate conditions

The widely perceived failure of 19th‐century expeditions to find and transit the Northwest Passage in the Canadian Arctic is often attributed to extraordinary cold climatic conditions associated with the “Little Ice Age” evident in proxy records. However, examination of 44 explorers' logs for the western Arctic from 1818 to 1910 reveals that climate indicators such as navigability, the distribution and thickness of annual sea ice, monthly surface air temperature, and the onset of melt and freeze were within the present range of variability.The quest for the Northwest Passage through the Canadian archipelago during the 19th century is frequently seen as a vain and tragic failure. Polar exploration during the Victorian era seems to us today to have been a costly exercise in heroic futility, which in many respects it was. This perspective has been reinforced since the 1970s, when paleoclimate reconstructions based on Arctic ice core stratigraphy appeared to confirm the existence of exceptionally cold conditions consistent with the period glaciologists had termed the “Little Ice Age” (Figure 1a), with temperatures more than one standard deviation colder relative to an early 20th‐century mean [Koerner, 1977; Koerner and Fisher, 1990; Overpeck et al., 1998]. In recent years, the view of the Little Ice Age as a synchronous worldwide and prolonged cold epoch that ended with modern warming has been questioned [Bradley and Jones, 1993; Jones and Briffa, 2001 ;Ogilvie, 2001].

Effects of surface freshwater flux induced by sea ice transport on the global thermohaline circulation

Effects of surface freshwater flux induced by sea ice formation and melting on the thermohaline circulation are investigated by using a sea‐ice‐ocean coupled general circulation model forced by monthly climatology. Restoring to the observed sea surface salinity is not employed in order to evaluate precisely the sea ice effects. Because of the model's improper representation of interaction between sea ice and the Northern Hemisphere deep convection, the discussion is focused on the effect of sea ice in the Southern Hemisphere. In the control case, deep water formation around Antarctica occurs under compact sea ice cover, where positive annual mean sea ice production is an essential factor to induce deep convection. When sea ice motion is turned off, deep water formation is maintained primarily by thermal destabilization of water columns, as annual mean sea ice production is almost zero everywhere. Consequently, the deep ocean around Antarctica is warmer and less saline compared with that for the control case, and the Atlantic bottom circulation is weakened by 16%. Northward salt transport from the Southern Ocean in the bottom layer also decreases. The amount of the decrease is greater by 1 order of magnitude than that of the surface salt input associated with sea ice. In a case where the freshwater flux at the ice‐ocean interface is turned off, results are similar to the case without sea ice transport, although surface heat and momentum fluxes significantly differ between them. This suggests that the influence of sea ice on freshwater flux is more important than on heat and momentum fluxes in affecting the global thermohaline circulation.