Picoplankton Carbon Biomass Assessments and Distribution of Prochlorococcus Ecotypes Linked to Loop Current Eddies During Summer in the Southern Gulf of Mexico

Abstract

Assessments of picoplankton carbon biomass in the pelagic ecosystem over the deep region of the southern Gulf of Mexico were conducted during three consecutive summer cruises. Notably, the relationship between carbon distribution of Prochlorococcus (PRO) and Loop Current (LC) dynamics was evaluated. Seawater samples were collected from the euphotic zone (~150 m) for estimating the abundance of the picoplankton populations using flow cytometry analyses. Carbon biomass estimates were based on cell abundance and variable conversion factors computed across stations and depths. On average, about half of the total depth-integrated carbon biomass of picoplankton was attributed to heterotrophic bacteria (HB, 54%) and three autotrophic populations (Prochlorococcus, Synechococcus, and pico-eukaryotes, 46%). In agreement with previous winter assessments, PRO was the dominant component of abundance (~90%) and pico-phytoplankton community biomass (>70%). Based on molecular analyses, distinct ecotypes of high-light PRO and low-light (LL) PRO were found within the euphotic zone, vertically distributed along light and nutrient gradients. Also, PRO distributions were related to hydrographic conditions strongly modulated by mesoscale dynamics. LL-PRO subgroups, located close to the nutricline under LL conditions, were associated with the westward propagation of anticyclonic eddies that episodically detach from the LC. This study highlights the role of the LC and its eddies in the transport and distribution of carbon biomass into the Gulf of Mexico, as represented by the deep subgroups of the dominant, tiniest autotroph within this oligotrophic ecosystem.

Water Mass Structure and Mixing Fractions in the Deepwater Region of the Gulf of Mexico

“…The sources of particulate organic matter that remineralize in the GoM probably originated to a large extent in surface oligotrophic waters, where Prochlorococcus and Synechococcus dominate the biomass of autotrophic picoplankton (Linacre et al., 2019) and where diazotrophic phytoplankton occasionally bloom (Holl et al., 2007; Mulholland et al., 2006). The results of Howe et al.…”

Do Loop Current eddies stimulate productivity in the Gulf of Mexico?

“…PP tot consists of two components: new production PPN tot fueled by nutrients supplied from a source external to the mixed layer and regenerated production PPR tot sustained by recycled nutrients within the euphotic layer (Dugdale and Goering, 1967;Eppley and Peterson, 1979). The euphotic depth corresponds to 1 % of the incoming photosynthetic active radiation at surface and reaches between 120 and 150 m in the GoM (Jolliff et al, 2008;Linacre et al, 2019). > 250 km from the LCEs' centers).…”

Cell carbon content and biomass assessments of dinoflagellates and diatoms in the oceanic ecosystem of the Southern Gulf of Mexico

“…It can also be associated with the detached Loop Current eddies (LCEs) propagating to the western basin [ 34 ], which are likely transporting Caribbean species into gulf waters. Concerning tropical intrusion, the transport of pico-phytoplankton populations, particularly the low-light Prochlorococcus ecotypes trapped inside LCEs in summer, was recently evidenced in SGoM waters [ 61 ]. Hence, it is reasonable to assume that the peak biomass of dinoflagellates recorded during MF2 at Perdido ( Fig 10 ) were likely influenced by the arrival of warmer eddies to this region.…”

“…During winter, a biomass average (± SD) of 24.57 ± 7.62 μg C L -1 has been reported for pico-phytoplankton populations living within the euphotic zone of SGoM oceanic waters [ 67 ]. This mean value decreased as warmer spring/summer conditions developed (6.3 ± 4.1 μgC L -1 ) and was dominated by Prochlorococcus populations [ 61 ]. These values suggest that dinoflagellates and diatoms do not contribute substantially to the total algal community, at least in the oceanic region.…”