Research Document - 2014/105

Environmental Conditions in the Labrador Sea during 2013

By I. Yashayaev, E.J.H. Head, K. Azetsu-Scott, M. Ringuette, Z. Wang, J. Anning, and S. Punshon

Abstract

The North Atlantic Oscillation (NAO) index for the December-January-February period of 2012-2013 was moderately negative, which is a significant reduction from the analogous period of 2011-2012. During the previous two years, the NAO index was close to the level in the early 1990s, a period characterized by the highest values in the last two decades. The National Centers for Environmental Prediction reanalysis of surface air temperature also indicated above normal conditions with an anomaly ranging between 3 to 7°C above normal in the Labrador Sea during the winter period; about 0.5°C above normal for the most of Labrador Sea during the spring; approximately 0 to 0.5°C above normal for the summer period; with an anomaly of -2 to 0.5°C during the fall period. The negative anomalies were mostly in the Baffin Bay/Davis Strait area north of the Labrador Sea, and the central and eastern portion of Labrador Sea region had mostly positive anomalies, though the magnitudes of the anomalies are relatively small. Sea surface temperature anomalies in the Labrador Sea followed the pattern observed in the air temperature: positive (1 to 6°C) in the winter and positive (about 0.5°C) in the summer. The Labrador Shelf ice concentration was below normal in January and March of 2013 (reference period: 1979-2000), while in February 2013, the ice concentration was higher than normal for the northwestern part of Labrador Shelf. Winter time convection in 2013 reached to 1000 m, which is significantly shallower than the 1400 m seen in the previous year, although still deeper than in the years of reduced convective activity (e.g., 2007 and 2011). The 1000-1500 m layer of the central Labrador Sea has been gradually warming since 2012. Under the warming trend, the winter ice extent has also decreased on the Labrador shelf. Increasing Total Inorganic Carbon and decreasing pH react as predicted by absorbing the excess anthropogenic atmospheric CO₂. Phytoplankton blooms on the shelves, which occur following stratification caused by ice-melt, generally occur earlier than those in the central basin, where stratification is more the result of surface warming. Despite an increase in the magnitude of the spring blooms, when averaged over the year the chlorophyll a biomass has tended to decline. The earlier and more intense production in the spring is certainly beneficial for the Calanus spp. younger stages, but the overall annual average decrease in chlorophyll could also be reflected in a decrease in total annual copepod abundance.

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