Seasonal flux patterns of planktonic foraminifera in a deep, oligotrophic, marginal sea: Sediment trap time series from the Gulf of Aqaba, northern Red Sea

N. Chernihovsky, A. Torfstein*, A. Almogi-Labin

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

15 Scopus citations

Abstract

Annual and interannual planktonic foraminifera (PF) fluxes, species assemblage composition, vertical distribution (0–600 m) and shell-size-distribution (63–125, 125–500, 500–1000 µm) were characterized in the marginal oligotrophic Gulf of Aqaba (GOA), northern Red Sea, between January 2014 and February 2016 using a monthly resolved sediment trap time series. PF fluxes in the GOA demonstrate strong seasonality, with low values observed during summer months, gradually increasing during the autumn-winter. This increase is coeval with decreasing sea-surface temperatures and deepening of the mixed layer depth in the GOA that drives the admixing of nutrient-replete subsurface waters into the mixed layer. This in turn, triggers an increase in primary productivity, expressed by enhanced chlorophyll-a concentrations. Spinose species constitute the majority of the PF assemblage. The dominant shell size-fraction is between 63 and 125 µm (~86% of the total flux), which has generally been overlooked in previous studies, resulting in a significant knowledge gap related to the neanic stages and the small-adult-size PF. Indeed, the 63–125 µm size-fraction is dominated by the smallest species Turborotalita clarkei (36–92% of this size fraction). The 125–500 µm size-fraction (~13%) is dominated by the species Globigerinoides ruber, while less than 1% of the shells are in the range of 500–1000 µm, dominated by Orbulina universa. Over the last few decades, the already low number of PF species decreased in the GOA from 13 to 10, including the disappearance of Trilobatus sacculifer, the most common species in the GOA during the 1970s. This finding could reflect the sensitivity of the geographic location of the GOA, at the edge of a > 2000 km transect that begins in the productive Arabian Sea, and spans across the Red Sea, where a gradual decrease in nutrient availability and increase in surface salinity imposes a corresponding decrease in PF species richness, abundances and diversity. Thus, the northern GOA is an extreme case of an oligotrophic system whose ecosystem is already pre-screened by the Red Sea transect. Combined with previous episodes of Trilobatus sacculifer disappearance identified in downcore records in the Red Sea, we conclude that the change in the PF community over recent decades is probably not the result of local eutrophication processes, as has been suggested in recent studies, but rather, more likely reflects environmental changes on a larger regional to global scale.

Original languageAmerican English
Pages (from-to)78-94
Number of pages17
JournalDeep-Sea Research Part I: Oceanographic Research Papers
Volume140
DOIs
StatePublished - Oct 2018

Bibliographical note

Publisher Copyright:
© 2018 Elsevier Ltd

Keywords

  • Gulf of Aqaba
  • Oligotrophic marginal sea
  • Planktonic foraminifera
  • Red Sea
  • Sediment traps
  • Turborotalita clarkei

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