Abstract
Abstract. A large anomalously warm water patch (the “Blob”) appeared in the NE Pacific Ocean in the winter of 2013–2014 and persisted through 2016 causing strong positive upper ocean temperature anomalies at Ocean Station Papa (OSP, 50∘ N, 145∘ W). The effect of the temperature anomalies on annual net community production (ANCP) was determined by upper ocean chemical mass balances of O2 and dissolved inorganic carbon (DIC) using data from a profiling float and a surface mooring. Year-round oxygen mass balance in the upper ocean (0 to 91–111 m) indicates that ANCP decreased after the first year when warmer water invaded this area and then returned to the “pre-Blob” value (2.4, 0.8, 2.1, and 1.6 mol C m−2 yr−1 from 2012 to 2016, with a mean value of 1.7±0.7 mol C m−2 yr−1). ANCP determined from the DIC mass balance has a mean value that is similar within the errors as that from the O2 mass balance but without a significant trend (2.0, 2.1, 2.6, and 3.0 mol C m−2 yr−1 with a mean value of 2.4±0.6 mol C m−2 yr−1). This is likely due to differences in the air–sea gas exchange, which is a major term for both mass balances. Oxygen has a residence time with respect to gas exchange of about 1 month while the CO2 gas exchange response time is more like a year. Therefore the biologically induced oxygen saturation anomaly responds fast enough to record annual changes, whereas that for CO2 does not. Phytoplankton pigment analysis from the upper ocean shows lower chlorophyll a concentrations and changes in plankton community composition (greater relative abundance of picoplankton) in the year after the warm water patch entered the area than in previous and subsequent years. Our analysis of multiple physical and biological processes that may have caused the ANCP decrease after warm water entered the area suggests that it was most likely due to the temperature-induced changes in biological processes.
Highlights
Net community production (NCP) in the upper ocean is defined as net organic carbon production, which equals biological production minus respiration
annual net community production (ANCP) determined from the dissolved inorganic carbon (DIC) mass balance has a mean value that is similar within the errors as that from the
Mass balance is higher because it includes the organic carbon that is degraded between the mixed layer and pycnocline in summer, so the ANCP from the DIC mass balance (4year mean: 2.4 ± 0.5 mol C m−2 yr−1 ) is very similar to the mixed layer ANCP determined from our oxygen mass balance model (4-year mean: 2.4 ± 0.9 mol C m−2 yr−1 ) and the mixed layer ANCP determined by Fassbender et al (2016)
Summary
Net community production (NCP) in the upper ocean is defined as net organic carbon production, which equals biological production minus respiration. At a steady state when integrated over a period of at least 1 year, the annual NCP (ANCP) is equivalent to the flux of biologically produced organic matter from the upper ocean to the interior Both biological production and respiration processes are temperaturedependent, and heterotrophic activities such as community respiration and zooplankton grazing are usually considered to be more sensitive to temperature change than autotrophic production (Allen et al, 2005; Brown et al, 2004; Gillooly et al, 2001; López-Urrutia et al, 2006; Regaudie-De-Gioux and Duarte, 2012; Rose and Caron, 2007). S. Wong et al, 2002b), and oxygen mass balance (Bushinsky and Emerson, 2015; Emerson, 1987; Emerson et al, 1991, 1993; Giesbrecht et al., 2012; Juranek et al, 2012; Plant et al, 2016)
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