Research Document - 2015/027

Optical, chemical, and biological oceanographic conditions on the Newfoundland and Labrador Shelf during 2013

By P. Pepin, G. Maillet, S. Fraser, T. Shears, and G. Redmond

Abstract

Seasonal cycles in temperature and salinity properties at Station 27 (S27) have shifted with warm and fresh conditions persisting well into winter in recent years. Advancing seasonal cycles in physical conditions observed in recent years at S27 appear to result in earlier spring drawdown and delayed recycling of macronutrient levels of silicate and nitrate that has traditionally occurred in the early autumn. Consequently, seasonally-adjusted annual anomalies of shallow and deep inventories of these macro-nutrients at S27 and across the sections are well below the annual climatology since 2009‑10 and in 2013, were approaching 3 standard deviation units below normal. In general, inventories of chlorophyll a (proxy for phytoplankton standing stock) at S27 and across sections remain below normal in recent years and were at the lowest level observed in the time-series at S27 in 2013. Overall, the amplitude (peak intensity) and magnitude (integrated chla biomass) of the spring bloom was below normal across most of the Newfoundland and Labrador (NL) sub-regions in 2013 compared to the climatology (1999‑2010). The initiation of the spring bloom was delayed on the southern Labrador and northeast Shelf resulting in reduced duration. The other sub-regions showed consistent timing indices with the exception of Hibernia that initiated substantially earlier resulting in a long duration bloom. The abundance of Oithona similis, Pseudocalanus sp. and Triconia sp. is at or near record levels of abundance from the Bonavista Bay to the southern Grand Banks sections. The abundance of Calanus glacialis and Calanus hyperboreus has shown long-term declines in abundance on the Flemish Cap and southeast Grand Bank starting in 2001, and shorter term declines on the Bonavista Bay and Seal Island section since 2009. Copepodite biomass at S27 in 2011‑13, based on the abundance of 8 dominant taxa, has demonstrated a consistent decline over time to a record low value in 2013 since the record high levels observed in 2009. Analysis of seasonal patterns in abundance reveals dramatic shifts in phenology of ecologically-important copepod species such as C. finmarchicus and Pseudocalanus sp. have occurred at S27 starting approximately in 2005, when the fall cohorts increase in relative abundance. The overall pattern of variation among the three trophic levels surveyed in this report (nutrients, phytoplankton biomass, and zooplankton abundance) does not reveal any clear association among trophic levels but consistency in some trends may be starting to provide new insights into trophic relationships.

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