ALBERT

Description: The transition from benthos to plankton requires multiple adaptations, yet so far it remains unclear how these are acquired in the course of the transition. To investigate this process, we analyzed the genetic diversity and distribution patterns of a group of foraminifera of the genus Bolivina with a tychopelagic mode of life (same species occurring both in benthos and plankton). We assembled a global sequence dataset for this group from single-cell DNA extractions and occurrences in metabarcodes from pelagic environmental samples. The pelagic sequences all cluster within a single monophyletic clade within Bolivina. This clade harbors three distinct genetic lineages, which are associated with incipient morphological differentiation. All lineages occur in plankton and benthos, but only one lineage shows no limit to offshore dispersal and has been shown to grow in the plankton. These observations indicate that the emergence of buoyancy regulation within the clade preceded the evolution of pelagic feeding and that the evolution of both traits was not channeled into a full transition into the plankton. We infer that in foraminifera, colonization of the planktonic niche may occur by sequential cooptation of independently acquired traits, with holoplanktonic species being recruited from tychopelagic ancestors.

Description: We present a new coccolithophore productivity reconstruction spanning the last 300 ka in core GeoB12613-1 retrieved from the western tropical Indian Ocean (IO), an area that mainly derives its warm and oligotrophic surface waters from the eastern IO. Application of a calibrated assemblage-based productivity index indicates a reduction in estimated primary productivity (EPP) from 300 ka to the present, with reconstructed EPP values ranging from 91 to 246 g C/m2/yr. Coccolithophore assemblages and coccolith fraction Sr/Ca indicate three main phases of productivity change, with major changes at 160 and 46 ka. The productivity and water-column stratification records show both dominant precession and obliquity periodicities, which appear to control the paleoproductivity in the study area over the last two glacial-interglacial cycles. Shallowing of the thermocline due to strengthening of the trade winds in response to insolation maxima resulted to peaks in EPP. Comparison with the eastern IO productivity and stratification coccolithophore data reveals good correspondence with our records, indicating a strong tropical Pacific influence in our study area. Both of these records show high productivity from 300 ka to 160 ka, interpreted to be due to stronger Walker Circulation while the declining productivity from 160 ka to the present day is a consequence of its weakening intensity.

Description: The chronology of deglacial meltwater pulses from the Laurentide Ice Sheet is well documented. However, the deglacial history of the North American-Arctic (north-eastern Laurentide and Innuitian) and western Greenland ice sheets draining into the Labrador Sea via Baffin Bay is less well constrained. Here we present new high-resolution, radiocarbon-dated records from the central Baffin Bay spanning ~17 to 10 kyr BP and documenting the full deglacial history of Baffin Bay. Sedimentological and geochemical data confirm the presence of two periods of enhanced detrital carbonate delivery, termed Baffin Bay Detrital Carbonate Events (BBDCs). These events are dated to ~14.2-13.7 kyr BP and ~12.7-11 kyr BP. They are synchronous across Baffin Bay and their mineralogical signature indicates a common source of detrital carbonate from northern Baffin Bay. The first event, BBDC 1, postdates Heinrich Event 1 and the second event, BBDC 0, predates the recently revised timing of Heinrich Event 0. The onset of the BBDC events appears not to be systematically linked to Greenland temperature change as they occur during both interstadial and stadial periods. This indicates that deglaciation of North American-Arctic and western Greenland ice sheets with the associated iceberg and meltwater discharge were decoupled from the dominant North Atlantic climate mode, where iceberg discharge events from the Laurentide Ice Sheet occurred during stadial periods.

Description: The Red Sea is an extreme marine environment, with conditions limiting the application of standard geochemical proxies for the reconstruction of paleoclimate. In order to develop paleoenvironmental reconstruction methods which are not dependent on chemical signals, we investigated the distribution of planktonic foraminifera in the surface sediments and assessed the viability of constructing foraminiferal transfer functions in this basin. We find a distinct gradient in the faunal assemblage along the basin's axis, which is reflected in a high correlation between faunal composition and all considered environmental parameters (temperature, salinity, chlorophyll a concentration, stratification, and oxycline depth). As a result, transfer functions constructed by different methods (ANN, MAT, IKM, WA-PLS) appear to be able to estimate all of these parameters with a high average accuracy (15% of the parameter's range in the Red Sea). However, redundancy analysis of the distribution of foraminiferal assemblages in surface sediments alone did not yield unambiguous results in terms of which of the considered factors exerts a primary control on the foraminifera distribution and which of the observed relationships are the result of the mutual correlation among the environmental factors. To disentangle the effect of individual environmental parameters, we applied the obtained transfer functions on a newly generated Holocene record from the central Red Sea. The integration of published paleoclimate reconstructions with our data allowed us to identify productivity as the most likely primary control of the planktonic foraminifera distribution in the Red Sea. The generated transfer functions can estimate paleoproductivity with acceptable accuracy (RMSEP chlorophyll a = 0.1 mg/m**3; ~ 8% of recent range), but only under such conditions in the past when circulation patterns and salinity levels in the basin were fundamentally comparable to the present day. Since productivity in the central and southern Red Sea is closely linked with the Monsoon-driven water exchange across the Strait of Bab al Mandab, the resulting reconstructions can provide indirect information on the mode and intensity of the monsoonal system in the past.

Description: Shallow marine ecosystems naturally experience fluctuating physicochemical conditions across spatial and temporal scales. Widespread coral-bleaching events, induced by prolonged heat stress, highlight the importance of how the duration and frequency of thermal stress influence the adaptive physiology of photosymbiotic calcifiers. Large benthic foraminifera harboring algal endosymbionts are major tropical carbonate producers and bioindicators of ecosystem health. Like corals, they are sensitive to thermal stress and bleach at temperatures temporarily occurring in their natural habitat and projected to happen more frequently. However, their thermal tolerance has been studied so far only by chronic exposure, so how they respond under more realistic episodic heat-event scenarios remains unknown. Here, we determined the physiological responses of Amphistegina gibbosa, an abundant western Atlantic foraminifera, to four different treatments--control, single, episodic, and chronic exposure to the same thermal stress (32°C)--in controlled laboratory cultures. Exposure to chronic thermal stress reduced motility and growth, while antioxidant capacity was elevated, and photosymbiont variables (coloration, oxygen-production rates, chlorophyll a concentration) indicated extensive bleaching. In contrast, single- and episodic-stress treatments were associated with higher motility and growth, while photosymbiont variables remained stable. The effects of single and episodic heat events were similar, except for the presumable occurrence of reproduction, which seemed to be suppressed by both episodic and chronic stress. The otherwise different responses between treatments with thermal fluctuations and chronic stress indicate adaptation to thermal peaks, but not to chronic exposure expected to ensue when baseline temperatures are elevated by climate change. This firstly implies that marine habitats with a history of fluctuating thermal stress potentially support resilient physiological mechanisms among photosymbiotic organisms. Secondly, there seem to be temporal constraints related to heat events among coral reef environments and reinforces the importance of temporal fluctuations in stress exposure in global-change studies and projections.

Description: The proliferation of key marine ecological engineers and carbonate producers often relies on their association with photosymbiotic algae. Evaluating stress responses of these organisms is important to predict their fate under future climate projections. Physiological approaches are limited in their ability to resolve the involved molecular mechanisms and attribute stress effects to the host or symbiont, while probing and partitioning of proteins cannot be applied in organisms where the host and symbiont are small and cannot be physically separated. Here we apply a label-free quantitative proteomics approach to detect changes of proteome composition in the diatom-bearing benthic foraminifera Amphistegina gibbosa experimentally exposed to three thermal-stress scenarios. We developed a workflow for protein extraction from less than ten specimens and simultaneously analysed host and symbiont proteomes. Despite little genomic data for the host, 1,618 proteins could be partially assembled and assigned. The proteomes revealed identical pattern of stress response among stress scenarios as that indicated by physiological measurements, but allowed identification of compartment-specific stress reactions. In the symbiont, stress-response and proteolysis-related proteins were up regulated while photosynthesis-related proteins declined. In contrast, host homeostasis was maintained through chaperone up-regulation associated with elevated proteosynthesis and proteolysis, and the host metabolism shifted to heterotrophy.