Regional differences in the timing of the spring bloom in the Labrador Sea

Abstract

The environmental factors that control the timing of the spring bloom in the Labrador Sea were investigated using ocean color data from satellites, historical oceanographic data and a primary production model. From the satellite data, the onset of the spring bloom was found to progress with the season from south to north, with the exception of the northern Labrador Sea. The onset for the northern Labrador Sea occurred at approximately the same time as in the southern Labrador Sea. Two possible factors for the regional differences were examined from the data: irradiance and mixedlayer depth (MLD). The early bloom in the northern Labrador Sea is related to the very shallow mixed layer associated with low-salinity water. The temporal variations of the mean chlorophyll concentration in 4 regions of the Labrador Sea (the Grand Banks, southern, central and northern Labrador Sea) during the growth phase of the spring bloom were modeled using a primary production model with MLD derived from historical temperature-salinity data. The temporal variations, in particular the early bloom in the northern Labrador Sea, were well reproduced by the model. A model sensitivity study showed that the onset of the spring bloom is highly sensitive to MLD. This confirms the finding from the data that MLD is a critical environmental factor for the spring bloom. The availability of the photosynthetically active radiation plays an important role, but is not a determining factor of the early bloom in the northern Labrador Sea. The sensitivity study also showed that pre-bloom oceanographic conditions and attenuation of light in water have a greater effect on the timing in a shallow mixed layer than in a deeper mixed layer. KEY WORDS: Spring bloom · Onset time · Mixed layer depth · Regional difference · Labrador SeaResale or republication not permitted without written consent of the publisher

Oxygen Saturation Surrounding Deep Water Formation Events in the Labrador Sea From Argo‐O2 Data

“…We illustrate the seasonal oxygen cycle in the Labrador Sea using a representative year of data (Figure ). The spring bloom timing, magnitude, and location vary as a result of physical forcings (freshwater stratification, eddy activity, temperature, and light; Frajka‐Williams & Rhines, ; Körtzinger et al, ; Wu et al, ). This bloom drives an increase in surface oxygen concentration and saturation anomaly (green bar in Figure ).…”

Physical controls and interannual variability of the Labrador Sea spring phytoplankton bloom in distinct regions

“…An early explanation of the reversal was offered by Head et al (2000), that ice melt from icebergs in the north Labrador Sea resulted in high stratification. A more recent study using a numerical model highlighted the importance of stratification for bloom timing patterns (Wu et al, 2008). Coincident in situ hydrographic and bio-optical measurements from a Seaglider during the 2005 spring bloom in the Labrador Sea also identified the importance of freshwater.…”

Physical controls and mesoscale variability in the Labrador Sea spring phytoplankton bloom observed by Seaglider

“…They used their observations to relate the bloom to zooplankton activity, and found that the timing of life cycles of the most abundant copepod, Calanus finmarchicus, corresponded to the time of the peak bloom, and that the region with the highest copepod biomass was the north bloom area. Two other papers on Labrador Sea spring bloom focus on bloom timing, one using SeaWiFS ocean color and a numerical model (Wu et al, 2008) and the other using SeaWiFS and hydrography (Frajka-Williams and Rhines, 2008). These studies have the advantage of a long, daily time series (1998-2003 and 1998-2008), but lack in situ observations to make a direct connection with water column stratification or dynamics.…”