Science Advisory Report  2016/041

Oceanographic conditions in the Atlantic zone in 2015

Summary

• Sea surface temperatures were above-normal in January and February in the ice-free southern portion of the zone, generally near-normal until June across the zone, below-normal to normal on the Labrador and Newfoundland shelf for the rest of the year but normal to above-normal elsewhere.
• Following a cold winter and late spring warming, sea surface temperatures increased to a record high in September for the satellite record (since 1985) overall in the Gulf of St. Lawrence.  September series records also occurred in the St. Lawrence Estuary and western Scotian Shelf, and near-record in eastern Gulf of Maine and Bay of Fundy.  Gulf of St. Lawrence fall sea surface cooling occurred two weeks later than normal. On the Newfoundland and Labrador Shelf, sea-surface temperatures remained normal to below normal.
• Sea-ice volume was near-normal when averaged over the ice season in the Gulf of St. Lawrence and the Newfoundland and Labrador Shelf, but extent was greater than normal during March and April off eastern Newfoundland and southern Labrador and in the Southern Gulf.  The ice season persisted up to five weeks later than normal, affecting the opening of the snow crab and lobster fisheries.
• Spring Cold Intermediate Layer (CIL) area was among the highest on record on the Grand Banks and remained slightly above normal in the summer but by late fall it had eroded to below normal values off eastern Newfoundland and completely eroded off southern Labrador.  In the Gulf of St. Lawrence spring CIL volume was not above normal in spite of the cold winter, and was warm and thin by August. On the Scotian Shelf, its volume was the 7th lowest in 42 years.
• Bottom temperatures were generally normal or above normal across the zone, including a near-record on the Scotian Shelf in 4V, and a 100-year record high in the deeper waters of the northern Gulf of St. Lawrence, where the bottom area covered with temperatures > 6°C has reached series records in Anticosti and Esquiman Channels.
• At the high-sampling frequency stations, the 0‑50 m average temperature was normal or above-normal.  Bottom temperatures were below-normal at Station 27, but above-normal elsewhere.  Record temperatures were achieved in both layers at Rimouski station.
• Stratification was below-normal at all high-sampling frequency stations except Halifax 2, and was at a record low at Shediac Valley.
• Deep nitrate inventories on the Newfoundland Shelf remained well below normal in 2015, maintaining a pattern that started in 2008/09, while they remained above normal throughout the Gulf of St. Lawrence, with record highs in the eastern and northern parts of the Gulf.  Nitrate inventories increased to above normal concentrations on the Scotian Shelf while they declined to below normal in the Bay of Fundy.
• Chlorophyll a inventories remained low in 2015 across the entire Newfoundland Shelf, continuing a pattern that started in 2011.  Chlorophyll a levels were near or above normal throughout the rest of the Zone, with a record high inventory in the northeastern Gulf of St. Lawrence.
• The onset of the spring phytoplankton bloom was later than normal throughout much of the Zone, likely as a result of a prolonged winter and above normal ice extent, although earlier blooms occurred in the northwest Gulf of St. Lawrence and on Georges Bank.
• Bloom magnitude was well below normal throughout much of the Zone except in the northern portions of the Gulf of St. Lawrence, St. Anthony Basin and Georges Bank.
• The bloom duration was generally shorter than normal throughout most of the Zone; however a record long spring phytoplankton bloom occurred in the northern Gulf of St. Lawrence.
• Abundance of Calanus finmarchicus was well below normal across the entire Zone, with the exception of the Flemish Cap Section, reaching record lows in parts of the Gulf of St. Lawrence and Scotian Shelf.
• Pseudocalanus sp. copepod abundance was well above normal across the Newfoundland Shelf and the Gulf of St. Lawrence but near or below normal on the Scotian Shelf.
• Copepod abundance demonstrated modest increases from 2014 to 2015, resulting in above average concentrations throughout much of the Zone, with the exception of the eastern and northern parts of the Gulf of St. Lawrence where abundances declined to below normal levels.
• The abundance of non-copepod zooplankton was above normal throughout most of the Zone, reaching record or near record levels throughout much of the Gulf of St. Lawrence.  This continues a trend that started around 2010‑12.
• The Labrador Current transport index was near normal over the Labrador and northeastern Newfoundland Slope and below normal over the Scotian Slope.
• Temperature and salinity profiles show that winter convective overturning in the central Labrador Sea reached a maximum depth of 1,850 m in 2015 following a maximum of 1,700 m in 2014.
• The 2015 convection is the deepest since the 2,400 m record-deep convection observed in 1994.  It produced the largest year class of Labrador Sea Water in the last two decades, containing increased concentrations of atmospheric gases (dissolved oxygen, anthropogenic gases, and carbon dioxide) which spread through the entire water mass (reaching 1,900 m in some places).
• Inter-annual variability in the cumulative surface heat loss and ocean heat content during the cooling seasons indicates that anomalously strong winter atmospheric cooling associated with the North Atlantic Oscillation is continuing to drive the recurrent convection in the Labrador Sea.
• Recurrent deep convection is contributing to decadal-scale variability in deep-water properties and transport across the subpolar North Atlantic and in the Atlantic Meridional Overturning Circulation.
• Anomalous bands of high phytoplankton abundance were observed in the eastern half of the Labrador Sea in 2015, and appeared to be aligned with horizontal gradients in seawater density across the AR7W line.

This Science Advisory Report is from the Eighteenth Annual Meeting of the Atlantic Zone Monitoring Program (AZMP) held March 15‑18, 2016.  Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

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