Temporal variability of dissolved iron species in the mesopelagic zone at Ocean Station PAPA

Warm Events Induce Loss of Resilience in Organic Carbon Production in the Northeast Pacific Ocean

“…Briefly, a more stratified winter minimizes the dilution of phytoplankton cells by vertical mixing; as a consequence, the cells remain in the surface layer at higher density and elevated rates of primary production start earlier in the year. Increased winter stratification should have constrained iron renewal in the upper ocean, which is the bottom-up control on primary production during late summer (Lam et al, 2006;Schallenberg et al, 2017;Westberry et al, 2016). According to the model, the period of enhanced production had an increase in zooplankton biomass, and the grazing pressure upon phytoplankton cells contributed to the primary production decline toward summer.…”

“…The study area lies within the eastern sector of the Gulf of Alaska and is known to have been continuously affected by ocean-atmospheric oscillations in the past decades, such as El Niño and PDO events (Lipsen et al, 2007;Whitney & Freeland, 1999;Wong et al, 2007). Primary production is relatively low during the summer due to iron limitation (Boyd & Harrison, 1999;Lam et al, 2006;Martin & Fitzwater, 1988;Miller et al, 1991;Schallenberg et al, 2015Schallenberg et al, , 2017; on the other hand, nitrate concentrations are always above detection limits (Westberry et al, 2016;Whitney & Freeland, 1999). During the winter, vertical mixing can reach as deep as 140 m and supplies the upper ocean with nutrients that fuel primary production toward spring and summer, when the MLD shoals to <20 m (Boyd & Harrison, 1999;Peña & Varela, 2007;Ribalet et al, 2010;Westberry et al, 2016;Whitney & Freeland, 1999).…”

“…The original iron data used in this manuscript are available at Schallenberg et al (2017) Appendix A and Nishioka et al (2001). The reduction in organic carbon production in the northeast Pacific is apparently forced by the absence of iron renewal with mixing during winters, leading to a loss of resilience in the system with extended periods of stratification.…”

“…During the winter, vertical mixing can reach as deep as 140 m and supplies the upper ocean with nutrients that fuel primary production toward spring and summer, when the MLD shoals to <20 m (Boyd & Harrison, 1999;Peña & Varela, 2007;Ribalet et al, 2010;Westberry et al, 2016;Whitney & Freeland, 1999). Primary production is relatively low during the summer due to iron limitation (Boyd & Harrison, 1999;Lam et al, 2006;Martin & Fitzwater, 1988;Miller et al, 1991;Schallenberg et al, 2015Schallenberg et al, , 2017; on the other hand, nitrate concentrations are always above detection limits (Westberry et al, 2016;Whitney & Freeland, 1999). 1976-1977, 1982-1983, 1986-1987, 1991-1992, 1997-1998, 2010-2011, and 2015-2016 El Niño events, while orange dots show the winter 2013-2014 and 2014-2015 Warm Blob event in the northeast Pacific.…”

“…Profiles of (a) nitrate (μM) and (b) dissolved iron concentrations (nM). Nitrate profiles from 2012 and 2013 are from biogeochemical floats included in our study, and iron data from the 2012 and 2013 cruises were originally published inSchallenberg et al (2015) and extracted from theSchallenberg et al (2017) Appendix A. Data from the remaining cruises were originally published inNishioka et al (2001).…”