End Of Polar Night Research Articles

Coastal Polynya Disrupts the Acoustic Backscatter Diurnal Signal Over the Eastern Laptev Sea Shelf

The diel vertical migration (DVM) of zooplankton is one of the largest species migrations to occur globally and is a key driver of regional ecosystems and the marine carbon pump. The dramatic changes in the Arctic environment in recent years, mainly associated with sea-ice decline, may have wide significance for the Arctic shelf ecosystems including DVM. Observations have revealed the occurrence of DVM in ice-covered Arctic waters, however, there have yet to be observations of DVM from the extensive Siberian shelves in the Eurasian Arctic and no analysis of how the sea-ice decline may affect DVM. Here, 2 yearlong time series of acoustic backscatter, collected by moored acoustic Doppler current profilers in the eastern Laptev Sea from August 1998 to August 1999, were used to examine the annual cycle of acoustic scattering, and therefore the annual cycle of DVM in the area. The acoustic time series were used along with atmospheric and oceanic reanalysis and satellite data. Our observations show that DVM did not occur during polar night and polar day, but is active during the spring and fall transition periods when there is a diurnal cycle in light conditions. DVM began beneath the fast ice at the end of polar night and increased in intensity through spring. However, the formation of a large polynya along the landfast ice edge in late March 1999 caused DVM to abruptly cease near the fast ice edge, while DVM persisted through spring to the start of polar day at the onshore mooring. We associate this cessation of synchronized DVM ∼1 month ahead of polar day with a predator-avoidance behavior of zooplankton in response to higher polar cod abundance near the polynya. During polar day, the intensity of acoustic scattering was attributed to the riverine suspended particles. Overall, our results highlight the occurrence of DVM on the Siberian shelves, the cessation of synchronized DVM when a polynya opens up nearby, and the potential impact of significant trends toward a more extensive Laptev Sea polynya as part of changing ice conditions in the Eurasian Arctic and their impact on the Arctic shelf ecology.

Diversity and Vertical Distribution of Microbial Eukaryotes in the Snow, Sea Ice and Seawater Near the North Pole at the End of the Polar Night

Our knowledge about the microorganisms living in the high Arctic Ocean is still rudimentary compared to other oceans mostly because of logistical challenges imposed by its inhospitable climate and the presence of a multi-year ice cap. We have used 18S rRNA gene libraries to study the diversity of microbial eukaryotes in the upper part of the water column (0–170 m depth), the sea ice (0–1.5 m depth) and the overlying snow from samples collected in the vicinity of the North Pole (N88°35′, E015°59) at the very end of the long polar night. We detected very diverse eukaryotes belonging to Alveolata, Fungi, Amoebozoa, Viridiplantae, Metazoa, Rhizaria, Heterokonta, and Telonemia. Different alveolates (dinoflagellates and Marine Alveolate Groups I and II species) were the most abundant and diverse in gene libraries from water and sea ice, representing 80% of the total number of clones and operational taxonomic units. Only contaminants and/or species from continental ecosystems were detected in snow, suggesting wind- and animal- or human-mediated cosmopolitan dispersal of some taxa. By contrast, sea ice and seawater samples harbored a larger and more similar inter-sample protist diversity as compared with snow. The North Pole was found to harbor distinctive eukaryotic communities along the vertical gradient with an unparalleled diversity of core dinoflagellates, largely dominant in libraries from the water column, as compared to other oceanic locations. In contrast, phototrophic organisms typical of Arctic sea ice and plankton, such as diatoms and prasinophytes, were very rare in our samples. This was most likely due to a decrease of their populations after several months of polar night darkness and to the presence of rich populations of diverse grazers. Whereas strict phototrophs were scarce, we identified a variety of likely mixotrophic taxa, which supports the idea that mixotrophy may be important for the survival of diverse protists through the long polar night.

Polar thermosphere-stratosphere photochemical coupling experiment: Two rocket measurements in polar winter at 69°N

Two rocket experiments were carried out just before and after the polar night at Andoya (69°N), Norway to investigate transport of nitric oxide produced by auroral processes into the middle atmosphere and its influence on the ozone chemistry. Nitric oxide densities of (2−5) × 108 cm−3 found in the 70–90 km region are one to two orders of magnitude larger than those at middle latitudes. The measured density profiles appear to agree semi-quantitatively with model simulations which includes auroral processes. The influence on ozone densities in the 70–90 km region due to such enhanced nitric oxide abundance is found to be still insignificant as compared to that due to transport in the middle of February, one month after the end of polar night and one month before the spring equinox. The larger ozone densities found in February (in spite of longer sunlit duration) than in November in the 40–60 km region again support predominance of transport over photochemical destruction.

A possible role of galactic cosmic rays in chlorine activation during polar night

Observations indicate that extremely low concentrations of HCl prevail in the stratosphere just after the end of polar night in Antarctica. This is mostly explained by the fast heterogeneous reactions of HCl with ClONO2 and HOCl. Just prior to polar night normal gas phase partitioning indicates that HOCl and ClONO2 constitute only about 30% of the inorganic chlorine reservoir, the major portion being HCl. Thus about 60% of the initial HCl would remain (after titration with HOCl and ClONO2) by the end of polar night. We suggest that further processing may be effected through the reaction of N2O5 with HCl on polar stratospheric cloud surfaces, the N2O5 being produced from NO radicals formed by the action of galactic cosmic rays. The efficiency of this process is controlled by the relative rate of the competing heterogeneous reaction of N2O5 with H2O. Moreover, galactic cosmic rays form OH radicals that further augment HCl processing. Through model calculations we show that this mechanism can considerably enhance the conversion of HCl into active chlorine, leading to an almost 50% lower HCl concentration shortly after the end of polar night compared to cases where galactic cosmic rays were neglected.