Annual cycles of phytoplankton chlorophyll concentrations in the global ocean: A satellite view

Abstract

Conceptual and mathematical models show that annual cycles of phytoplankton biomass are different within different regions of the ocean. The purpose of this manuscript is to use coastal zone color scanner chlorophyll imagery (CZCS-Chl) to determine annual cycles in phytoplankton chlorophyll (biomass) averaged over very large areas of the global ocean. A possible result is that large-scale averaging of CZCS-Chl will yield no interpretable signals because of spatial variability in annual cycles at scales much smaller than our averaging scale. Alternatively, if our analyses show regular and persistent global patterns, then our results will provide a basin-scale overview of phytoplankton biomass seasonality for comparison with model results or with other large-scale oceanographic measurements. Our results show that monthly mean CZCS-Chl imagery (and using in situ concentrations for winter at latitudes poleward of 40 deg) resolves important differences in annual phytoplankton chlorophyll cycles for different ocean basins and latitude belts. As predicted by simple models of plankton dynamics, our results show: (1) global subtropical waters have circa 2X higher CZCS-Chl concentrations in winter than in summer and (2) subpolar waters in the northern hemisphere (NH) have mean monthly CZCS-Chl concentrations during May and June that are manyfold higher than in winter, particularly in the North Atlantic. Our results also show: (1) Northern Indian Ocean is the major Copyright 1993 by the American Geophysical Union. Paper number 93GB02358. 0886-6236/93/92GB-02358510.00 subtropical anomaly, (2) subpolar waters in the SH do not show differences between spring maxima and winter minima as large as those in the subpolar NH and (3) larger ocean area in the SH is compensated by higher mean annual CZCS-Chl concentrations in the NH, so that annual hemispherical integrals (mean annual concentrations multiplied by ocean areas) are very similar. The simple patterns we report imply that mean annual cycles in phytoplankton biomass averaged over very large areas of the global ocean are largely explainable by very simple mathematical models such as those presented several decades ago by Cushing, Riley, Steele, and others. z CTIC PERATE TROPICAL ß J F M A M J J A S O N D MONTH

Biological Oceanography by Remote Sensing

“…This hemispherical asymmetry may be due to differences in micronutrient (iron) availability, solar irradiance, vertical mixing, or zooplankton grazing. Overall, the seasonal patterns found by Yoder et al 35 are consistent with predictions based on simple models of predator -prey (zooplankton -phytoplankton) interactions with implicit assumptions about growth limitation by nutrients and solar irradiance. In some respects this agreement is surprising as there is considerable spatial and temporal variability in the distribution of phytoplankton (section 4.3).…”

“…Yoder et al 35 have used the monthly CZCS chlorophyll concentration values to look at the biological seasonal cycle in the oceans on a global scale. They averaged the data spatial into latitude bands, defining an equatorial band and northern and southern hemisphere subtropical and subpolar bands.…”

Upwelling in the Taiwan Strait during the summer monsoon detected by satellite and shipboard measurements

“…It repeats the same orbit every 16 days (233 orbits) and covers the same point on the earth every 1-2 days depending on the latitude (Yoder, McClain, Feldman, & Esaias, 1993). SeaWiFS data are particularly useful for determining Chl-a levels.…”

Primary productivity and its regulation in the Arabian Sea during 1995

“…In contrast to primary productivity, there are several seasonal analyses of chlorophyll from ship and satellite observations (Banse, 1987;Yoder et al, 1993;English, 1994, 2000;Longhurst, 1998). Banse (1987) and Banse and English (2000) treat the various subregions as de"ned by Colborn (1975) on the basis of seasonal thermal structure.…”

“…In the Arabian Sea, it not only forces upwelling of nutrient-rich subsurface water, but also provides a high #ux of iron-rich eolian dust to a tropical ocean that receives intense (saturating) solar radiation. These favorable conditions are maintained throughout the 3-to 3.5-month period of the SW Monsoon, resulting in a sustained high rate of primary productivity that is exceptional in its magnitude among o!shore ocean regions (Ryther and Menzel, 1965;Zeitzschel, 1973;Yoder et al, 1993). The processes responsible for this sustained high primary productivity during the SW Monsoon are strong and continuous upwelling (Currie et al, 1973;Smith and Bottero, 1977;, high subsurface nutrient concentrations (Ryther and Menzel, 1965;McGill, 1973), and high eolian iron supply through dust (Bauer et al, 1991;Smith, 1991).…”