Physical drivers of interannual chlorophyll variability in the eastern subtropical North Atlantic

Abstract

[1] Interannual chlorophyll variability and its driving mechanisms are evaluated in the eastern subtropical North Atlantic, where elevated surface chlorophyll concentrations regularly extend more than 1500 km into the central subtropical North Atlantic and modulate the areal extent of the North Atlantic's lowest chlorophyll waters. We first characterize the considerable interannual variability in the size of the high chlorophyll region using SeaWiFS satellite data. We then evaluate the relationship between satellite chlorophyll and sea surface height (SSH), which are anticorrelated in the study region, most likely as a result of the inverse relationship between SSH and nutricline depth. To put these results in a longer temporal context, we study a hindcast simulation of a global ocean model with biogeochemistry (GFDL's MOM4.1 with TOPAZ biogeochemistry), after evaluating the model's skill at simulating chlorophyll and SSH relative to observations. In the simulation, the variability seen during the satellite era appears to be imbedded in a much larger multidecadal modulation. The drivers of such variability are assessed by evaluating all the terms in the nutrient budget of the euphotic zone. Because diffusive processes are not a dominant control on nutrient supply, stratification is not a good indicator of nutrient supply. Rather, vertical advection of nutrients, strongly tied to Ekman pumping, is the leading driver of variability in the size of the high chlorophyll region and the productivity within the study area.

Potential impact of climate change on the Intra-Americas Sea: Part-1. A dynamic downscaling of the CMIP5 model projections

“…In the future, a regional biogeochemical ocean simulation is required to study the impact of GHG-induced warming on the ocean ecosystem in the IAS (Pastor et al, 2013). The future study will also benefit from the development of regional coupled atmosphere-ocean models (Li and Misra, 2014).…”

Causes of the Regional Variability in Observed Sea Level, Sea Surface Temperature and Ocean Colour Over the Period 1993–2011

“…In the eastern subtropical North Atlantic, between 10°N and 25°N, the negative correlation found between chlorophyll and SSH has been shown to result from an inverse relationship between SSH and nutricline depth (Pastor et al 2014). In this region, the changes in nutricline depth and nutrient supply to the surface are governed primarily by changes in Ekman pumping (driving vertical advection processes), rather than by changes in stratification.…”

Physical‐biological synchrony in the global ocean associated with recent variability in the central and western equatorial Pacific

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