Abstract The Mg/Ca of marine calcareous Planktic Foraminifera (PF) shells is commonly used for sea surface temperature reconstructions. However, compared to open marine environments, hypersaline (>40) oligotrophic seas have been shown to accommodate PF with higher Mg/Ca and divergent temperature to Mg/Ca relationships. To investigate influencing factors of PF Mg uptake in hypersaline regions, we measured the Mg/Ca of two flux‐dominating PF species, Globigerinoides ruber albus and Turborotalita clarkei, derived from a monthly resolved time series of sediment traps in the Gulf of Aqaba, northern Red Sea as well as the corresponding temperature, salinity, and pH values. The PF exhibit elevated Mg/Ca which cannot be explained by post‐deposition or interstitial sediment diagenetic processes. G. ruber albus displays Mg/Ca trends that strongly follow seasonal mixed layer temperature changes. Conversely, T. clarkei Mg/Ca trends do not follow temperature but rather show significant Mg/Ca enrichment following mixing of the surface water column. We present a framework for incorporating elevated Mg/Ca into global Mg/Ca‐T calibrations for G. ruber albus and present a new Mg/Ca‐T calibration suitable for hypersaline marine environments.

Planktonic foraminifera (PF) shells comprise a significant fraction of the global oceanic carbonate flux and serve as a primary archive of the history of the oceans. Yet, a limited understanding of their life cycles dynamics and biological rhythms, hampers their application as palaeoceanographic proxies. Here, we present the flux of ten PF species and their shell-size distributions at a daily timescale resolution in the Gulf of Aqaba (GOA), northern Red Sea. We report diameter measurements of ~13,500 shells, associated with ten PF species, retrieved using an automated time-series sediment trap deployed at a water depth of ~410 m (seafloor depth 610 m) throughout more than a full annual cycle between 2015 and 2016. Most of the PF species display a wide intraspecific shell-size distribution among adult PF, while six abundant species (G. ruber, G. rubescens + G. tenellus, G. glutinata, G. calida and G. siphonifera) display significantly smaller shell-sizes compared with corresponding specimens from sediment traps and seafloor sediments across other tropical, subtropical and upwelling regions. The results indicate that PF generation cycles can be classified according to three patterns: (1) Quiescent: minimal shell-size and extended life cycles due to unfavorable conditions and food scarcity when the water column is stratified and oligotrophic, (2) Transient: the gradual increase of Chlorophyll-a (Chl-a) concentrations and food availability enhance shorter life-cycles, although PF do not necessarily reach maximal shell-sizes, (3) Successive: PF fluxes and Chl-a concentrations are maximal, the generation time is extended and individuals might display growth to maximal shell-sizes.

The trace element chemistry of planktonic Foraminifera (PF) shells records the seawater composition and conditions of the marine environment in which they grow. Yet, long term in situ calibration and interspecies differences in proxy systematics are still poorly constrained, hampering the use of trace element distributions as environmental tracers of modern and past oceanic conditions. Here, we report element ratios using laser ablation mass spectrometry (LA-ICP-MS) in PF shells collected using monthly resolved sediment traps at various water column depths in the northern part of the Gulf of Aqaba (GOA) in 2014 and 2015. In particular, we focus on Calcium-normalized elemental abundances in different morphotypes of the two abundant species Globigerinoides ruber and Turborotalita clarkei . The results show that inter-chamber cation/Ca variability is lower in G. ruber relative to T. clarkei . In general, Mg/Ca in G. ruber display a positive correlation with temperature over time and depth. This general relationship does not exist in T. clarkei , which displays strong positive Mg/Ca perturbations in the subsurface water column, likely reflecting the impact of bottom sediment resuspension events during winter. B/Ca in G. ruber and T. clarkei displays a gradual first-order decrease over time that roughly corresponds with surface water p H patterns. By contrast, Sr/Ca remains constant around 1.5 mmol/mol between the chambers, species, and over time and different water depths. Al/Ca, Ti/Ca, Mn/Ca, and Fe/Ca co-vary, most likely reflecting the control of terrigenous end members, while B/Ca, Mg/Ca, and Na/Ca vary independently, each assumed to be controlled by different environmental processes. The results are evaluated in the context of oceanic properties and characteristic seawater trace element compositions, in order to improve their application as environmental tracers and paleo-proxies.

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.

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 gm) 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 mu m (similar to 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 mu m sizefraction is dominated by the smallest species Turborotalita clarkei (36-92% of this size fraction). The 125-500 mu m size-fraction (similar to 13%) is dominated by the species Globigerinoides ruber, while less than 1% of the shells are in the range of 500-1000 mu m, 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.