Budgets of nitrate, dissolved oxygen, and particulate organic carbon (POC) were constructed from data collected on-board a Lagrangian, profiling float deployed between April 4 and May 25, 2008, as part of the North Atlantic Bloom Experiment. These measurements were used to estimate net community production (NCP) and apparent export of POC along the float trajectory. A storm resulting in deep mixing and temporary suspension of net production separated the bloom into early (April 23–27) and main (May 6–13) periods over which ~264 and ~805 mmol C m^-2 were produced, respectively. Subtraction of the total POC production from the NCP yielded maximum estimates of apparent POC export amounting to ~92 and 574 mmol C m^-2 during the early and main blooms, respectively. The bloom terminated the following day and ~282 mmol C m^-2 were lost due to net respiration (70%) and apparent export (30%). Thus, the majority of the apparent export of POC occurred continuously during the main bloom and a large respiration event occurred during bloom Termination. A comparison of the POC flux during the main bloom period with independent estimates at greater depth suggest a rapid rate of remineralization between 60 and 100 m. We suggest the high rates of remineralization in the upper layers could explain the apparent lack of carbon overconsumption (C:N>6.6) in the North Atlantic during the spring bloom.

Freshening in the Canada basin of the Arctic Ocean began in the 1990s and continued to at least the end of 2008. By then, the Arctic Ocean might have gained four times as much fresh water as comprised the Great Salinity Anomaly of the 1970s, raising the spectre of slowing global ocean circulation. Freshening has been attributed to increased sea ice melting and contributions from runoff, but a leading explanation has been a strengthening of the Beaufort High — a characteristic peak in sea level atmospheric pressure — which tends to accelerate an anticyclonic (clockwise) wind pattern causing convergence of fresh surface water. Limited observations have made this explanation difficult to verify, and observations of increasing freshwater content under a weakened Beaufort High suggest that other factors must be affecting freshwater content.

Here we use observations to show that during a time of record reductions in ice extent from 2005 to 2008, the dominant freshwater content changes were an increase in the Canada basin balanced by a decrease in the Eurasian basin. Observations are drawn from satellite data (sea surface height and ocean-bottom pressure) and in situ data. The freshwater changes were due to a cyclonic (anticlockwise) shift in the ocean pathway of Eurasian runoff forced by strengthening of the west-to-east Northern Hemisphere atmospheric circulation characterized by an increased Arctic Oscillation index. Our results confirm that runoff is an important influence on the Arctic Ocean and establish that the spatial and temporal manifestations of the runoff pathways are modulated by the Arctic Oscillation, rather than the strength of the wind-driven Beaufort Gyre circulation.

Here we report the first optical, sensor-based profiles of nitrate from the central Makarov and Amundsen and southern Canada basins of the Arctic Ocean. These profiles were obtained as part of the International Polar Year program during spring 2007 and 2008 field seasons of the North Pole Environmental Observatory (NPEO) and Beaufort Gyre Exploration Program (BGEP). These nitrate data were combined with in-situ, sensor-based profiles of dissolved oxygen to derive the first high-resolution vertical NO profiles to be reported for the Arctic Ocean.

The focus of this paper is on the halocline layer that insulates sea ice from Atlantic water heat and is an important source of nutrients for marine ecosystems within and downstream of the Arctic. Previous reports based on bottle data have identified a distinct lower halocline layer associated with an NO minimum at about S=34.2 that was proposed to be formed initially in the Nansen Basin and then advected downstream. Greater resolution afforded by our data reveal an even more pronounced NO minimum within the upper, cold halocline of the Makarov Basin. Thus a distinct lower salinity source ventilated the Makarov and not the Amundsen Basin. In addition, a larger Eurasian River water influence overlies this halocline source in the Makarov. Observations in the southern Canada Basin corroborate previous studies confirming multiple lower halocline influences including diapycnal mixing between Pacific winter waters and Atlantic-derived lower halocline waters, ventilation via brine formation induced in persistent openings in the ice, and cold, O₂-rich lower halocline waters originating in the Eurasian Basin. These findings demonstrate that continuous sensing of chemical properties promises to significantly advance understanding of the maintenance and circulation of the halocline.