Seasonality of oceanic primary production and its interannual variability from 1998 to 2007 |
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| Affiliation: | 1. Center for Satellite Applications and Research, National Oceanic and Atmospheric Administration, College Park, MD, United States;2. Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD, United States;3. Division of Earth and Ocean Sciences, Nicholas School of the Environment, Duke University, Durham, NC, United States;1. South Eastern Area Laboratory Services, Sydney, NSW, Australia;2. School of Medical Sciences, the University of New South Wales, Sydney, NSW, Australia;3. Clinic 275, STD Services, Royal Adelaide Hospital, Adelaide, SA, Australia;4. UQ Centre for Clinical Research, University of Queensland, Brisbane, QLD 4029, Australia;5. Microbiology and Infectious Diseases Directorate, SA Pathology, Adelaide, SA, Australia;6. Pathology Queensland Central Laboratory, Brisbane, QLD, Australia;1. Department of Pediatrics, National Cheng Kung University Hospital, College of Medicine, National Cheng Kung University, Tainan City, Taiwan;2. Department of Emergency Medicine, National Cheng Kung University Hospital, College of Medicine, National Cheng Kung University, Tainan City, Taiwan;3. Center of Infectious Disease and Signaling Research, National Cheng Kung University, Tainan City, Taiwan;1. Department of Oceanography, Pusan, National University, Busan 46241, Republic of Korea;2. Department of Polar Remote Sensing, Korea Polar Research Institute, Incheon 21990, Republic of Korea;3. NOAA/NESDIC Center for Satellite Application and Reseaarch, Colledge Park, MD 20740, USA;5. Department of Marine & Fisheries Business and Economics, Pukyong National University, Busan 48513, Republic of Korea;1. Alaska Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, 17109 Pt. Lena Loop Rd., Juneau, AK 99801, USA;2. Pacific Marine Environmental Laboratory, Oceans and Atmospheric Research, National Oceanic and Atmospheric Administration, 7600 Sand Point Way NE, Seattle, WA 98115-0070, USA;3. Alaska Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, 7600 Sand Point Way NE, Seattle, WA 98115-0070, USA;4. University of Alaska Fairbanks, Juneau Center for Fisheries and Oceans, 17309 Pt. Lena Loop Rd., Juneau, AK 99801, USA |
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| Abstract: | The seasonality of primary productivity plays an important role in nutrient and carbon cycling. We quantify the seasonality of satellite-derived, oceanic net primary production (NPP) and its interannual variability during the first decade of the SeaWiFS mission (1998 to 2007) using a normalized seasonality index (NSI). The NSI, which is based upon production half-time, t(1/2), generally becomes progressively more episodic with increasing latitude in open ocean waters, spanning from a relatively constant rate of primary productivity throughout the year (mean t(1/2) ~5 months) in subtropical waters to more pulsed events (mean t(1/2) ~3 months) in subpolar waters. This relatively gradual, poleward pattern in NSI differs from recent estimates of phytoplankton bloom duration, another measure of seasonality, at lower latitudes (~40°S–40°N). These differences likely reflect the temporal component of production assessed by each metric, with NSI able to more fully capture the irregular nature of production characteristic of waters in this zonal band. The interannual variability in NSI was generally low, with higher variability observed primarily in frontal and seasonal upwelling zones. The influence of the El Niño–Southern Oscillation on this variability was clearly evident, particularly in the equatorial Pacific, where primary productivity was anomalously episodic from the date line east to the coast of South America in 1998. Yearly seasonality and the magnitude of annual production were generally positively correlated at mid-latitudes and negatively correlated at tropical latitudes, particularly in a region bordering the Pacific equatorial divergence. This implies that increases of annual production in the former region are attained over the course of a year by shorter duration but higher magnitude NPP events, while in the latter areas it results from an increased frequency or duration of similar magnitude events. Statistically significant trends in the seasonality, both positive and negative, were detected in various patches. We suggest that NSI be used together with other phenomenological characteristics of phytoplankton biomass and productivity, such as the timing of bloom initiation and duration, as a means to remotely quantify phytoplankton seasonality and monitor the response of the oceanic ecosystem to environmental variability and climate change. |
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| Keywords: | Seasonality Episodicity Oceanic primary productivity Satellite ocean color radiometry |
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