The daily resolved temperature dependence and structure of planktonic foraminifera blooms

N Chernihovsky,A Torfstein,A Almogi-Labin,S S Kienast

doi:10.1038/s41598-020-74342-z

Abstract

Planktonic foraminifera (PF) life cycles are highly sensitive to marine conditions, which are evolving rapidly due to anthropogenic climate change. Even though PF shells in the sedimentary record serve as prominent proxies of past ocean conditions, very little is still known about their life cycles, particularly in oligotrophic environments. Here, we present a full annual record of PF fluxes (> 63 µm) from the oligotrophic Gulf of Aqaba, northern Red Sea, sampled at daily timescales during 2015–2016 using an automated time-series sediment trap. These results are coupled with daily surface chlorophyll-a concentrations, sea surface temperatures (SSTs), particulate organic carbon and bulk fluxes, together with monthly resolved vertical profiles of chlorophyll-a, temperatures and nutrient concentrations. The annual cycle of PF fluxes is controlled by SST changes that drive water column mixing and changes in food availability. PF species flux patterns and succession dynamics vary throughout the year, displaying large variability on previously undocumented daily-weekly timescales, and are not synchronized with lunar periodicity. On daily timescales, spring blooms show a complex structure and interplay between SSTs, chlorophyll-a surface concentrations and PF fluxes. These events deliver about a third of the total annual PF flux over a period of several weeks.

Highlights

Planktonic foraminifera (PF) life cycles are highly sensitive to marine conditions, which are evolving rapidly due to anthropogenic climate change
Samples collected between 18.03.16 and 03.04.16 were not picked for PF due to extremely low bulk fluxes (Figs. 2, 3) and are considered to be devoid of PF shells
High resolution daily timescale time series of planktonic foraminifera fluxes, surface Chl-a concentrations, and sea surface temperatures (SSTs), supported by corresponding vertical profiles at lower resolution, suggest that seasonal PF flux patterns in the oligotrophic setting of the Gulf of Aqaba (GOA), northern Red Sea, are controlled by the temperature driven configuration of the water column, with approximately a third of the total annual PF flux delivered over a short period of ~ 4 weeks associated with the spring bloom

Summary

Introduction

Planktonic foraminifera (PF) life cycles are highly sensitive to marine conditions, which are evolving rapidly due to anthropogenic climate change. We present a full annual record of PF fluxes (> 63 μm) from the oligotrophic Gulf of Aqaba, northern Red Sea, sampled at daily timescales during 2015–2016 using an automated time-series sediment trap. Anthropogenic CO2 emissions are driving ocean acidification that has been suggested to impose reduced PF calcification rates, resulting in thinner shells and lower PF shell weights, and shifts in their assemblage composition, in pace with the warming trends of the last 150 years[6,7,8,9] This warrants the question of whether and how these organisms will be further affected by ongoing changes in environmental conditions. PF succession at the eastern Northern Atlantic is stimulated by redistribution of chlorophyll-a (Chl-a) and admixing of nutrient-enriched waters into the mixed layer, in concert with seasonal hydrographic changes[15]

Methods

Results

Discussion

Conclusion