Description: Sedimentary specimens of the planktonic foraminifera Globorotalia inflata can provide much needed information on subsurface conditions of past oceans. However, interpretation of its geochemical signal is complicated by possible effects of cryptic diversity and encrustation. Here we address these issues using plankton tow and sediment samples from the western South Atlantic, where the two genotypes of G. inflata meet at the Brazil-Malvinas Confluence Zone. The δ18O and δ13C of encrusted specimens from both genotypes from a core within the confluence zone are indistinguishable. However, we do find a large influence of encrustation on δ18O and Mg/Ca. Whereas crust Mg/Ca ratios are at all locations lower than lamellar calcite, the crust effect on δ18O is less consistent in space. Plankton tows show that encrusted specimens occur at any depth and that even close to the surface crust Mg/Ca ratios are lower than in lamellar calcite. This is inconsistent with formation of the crust at lower temperature at greater depth. Instead we suggest that the difference between the crust and lamellar calcite Mg/Ca ratio is temperature-independent and due to the presence of high Mg/Ca bands only in the lamellar calcite. The variable crust effect on δ18O is more difficult to explain, but the higher incidence of crust free specimens in warmer waters and the observation that a crust effect is clearest in the confluence zone, hint at the possibility that the difference reflects advective mixing of specimens from warmer and colder areas, rather than vertical migration.

Description: Species of planktonic foraminifera exhibit specific seasonal production patterns and different preferred vertical habitats. The seasonality and vertical habitats are not constant throughout the range of the species and changes therein must be considered when interpreting paleoceanographic reconstructions based on fossil foraminifera. Accounting for the effect of vertical and seasonal habitat tracking on foraminifera proxies at times of climate change is difficult because it requires independent fossil evidence. An alternative that could reduce the bias in paleoceanographic reconstructions is to predict species-specific habitat shifts under climate change using an ecosystem modeling approach. To this end, we present a new version of a planktonic foraminifera model, PLAFOM2.0, embedded into the ocean component of the Community Earth System Model, version 1.2.2. This model predicts monthly global concentrations of the planktonic foraminiferal species: Neogloboquadrina pachyderma, N. incompta, Globigerina bulloides, Globigerinoides ruber (white), and Trilobatus sacculifer throughout the world ocean, resolved in 24 vertical layers to 250m depth. The resolution along the vertical dimension has been implemented by applying the previously used spatial parameterization of biomass as a function of temperature, light, nutrition, and competition on depth-resolved parameter fields. This approach alone results in the emergence of species-specific vertical habitats, which are spatially and temporally variable. Although an explicit parameterization of the vertical dimension has not been carried out, the seasonal and vertical distribution patterns predicted by the model are in good agreement with sediment trap data and plankton tow observations. In the simulation, the colder-water species N. pachyderma, N. incompta, and G. bulloides show a pronounced seasonal cycle in their depth habitat in the polar and subpolar regions, which appears to be controlled by food availability. During the warm season, these species preferably occur in the subsurface, while towards the cold season they ascend through the water column and are found closer to the sea surface. The warm-water species G. ruber (white) and T. sacculifer exhibit a less variable shallow depth habitat with highest biomass concentrations within the top 40m of the water column. Nevertheless, even these species show vertical habitat variability and their seasonal occurrence outside the tropics is limited to the warm surface layer that develops at the end of the warm season. The emergence in PLAFOM2.0 of species-specific vertical habitats that are consistent with observations indicates that the population dynamics of planktonic foraminifera species may be driven by the same factors in time, space, and with depth, in which case the model can provide a reliable and robust tool to aid the interpretation of proxy records.

Description: Shell fluxes of planktonic Foraminifera species vary intra-annually in a pattern that appears to follow the seasonal cycle. However, the variation in the timing and prominence of seasonal flux maxima in space and among species remains poorly constrained. Thus, although changing seasonality may result in a flux-weighted temperature offset of more than 5° C within a species, this effect is often ignored in the interpretation of Foraminifera-based paleoceanographic records. To address this issue we present an analysis of the intra-annual pattern of shell flux variability in 37 globally distributed time series. The existence of a seasonal component in flux variability was objectively characterised using periodic regression. This analysis yielded estimates of the number, timing and prominence of seasonal flux maxima. Over 80% of the flux series across all species showed a statistically significant periodic component, indicating that a considerable part of the intra-annual flux variability is predictable. Temperature appears to be a powerful predictor of flux seasonality, but its effect differs among species. Three different modes of seasonality are distinguishable. Tropical and subtropical species (Globigerinoides ruber (white and pink varieties), Neogloboquadrina dutertrei, Globigerinoides sacculifer, Orbulina universa, Globigerinella siphonifera, Pulleniatina obliquiloculata, Globorotalia menardii, Globoturborotalita rubescens, Globoturborotalita tenella and Globigerinoides conglobatus) appear to have a less predictable flux pattern, with random peak timing in warm waters. In colder waters, seasonality is more prevalent: peak fluxes occur shortly after summer temperature maxima and peak prominence increases. This tendency is stronger in species with a narrower temperature range, implying that warm-adapted species find it increasingly difficult to reproduce outside their optimum temperature range and that, with decreasing mean temperature, their flux is progressively more focussed in the warm season. The second group includes the temperate to cold-water species Globigerina bulloides, Globigerinita glutinata, Turborotalita quinqueloba, Neogloboquadrina incompta, Neogloboquadrina pachyderma, Globorotalia scitula, Globigerinella calida, Globigerina falconensis, Globorotalia theyeri and Globigerinita uvula. These species show a highly predictable seasonal pattern, with one to two peaks a year, which occur earlier in warmer waters. Peak prominence in this group is independent of temperature. The earlier-when-warmer pattern in this group is related to the timing of productivity maxima. Finally, the deep-dwelling Globorotalia truncatulinoides and Globorotalia inflata show a regular and pronounced peak in winter and spring. The remarkably low flux outside the main pulse may indicate a long reproductive cycle of these species. Overall, our analysis indicates that the seasonality of planktonic Foraminifera shell flux is predictable and reveals the existence of distinct modes of phenology among species. We evaluate the effect of changing seasonality on paleoceanographic reconstructions and find that, irrespective of the seasonality mode, the actual magnitude of environmental change will be underestimated. The observed constraints on flux seasonality can serve as the basis for predictive modelling of flux pattern. As long as the diversity of species seasonality is accounted for in such models, the results can be used to improve reconstructions of the magnitude of environmental change in paleoceanographic records.

Description: To monitor particle fluxes and near bottom hydrographic variability a modified version of the benthic Bottom Boundary (BOBO) lander was deployed at 57° 29.09 N, 27° 54.53 W on the Gardar Drift at a water depth of 2630 m. The deployment lasted from 16/09/2007 to 19/09/2008. Current velocity (S and W; cm/s) and acoustic backscatter (counts) were monitored at 15-min intervals using an upward looking RD Instruments 1200-kHz ADCP. These are the data from 6.65 m above the seafloor. Full details about the deployment can be found in Jonkers et al., 2010 (doi:10.1016/j.dsr.2010.05.005).

Description: To monitor particle fluxes and near bottom hydrographic variability a modified version of the benthic Bottom Boundary (BOBO) lander was deployed at 57° 29.09 N, 27° 54.53 W on the Gardar Drift at a water depth of 2630 m. These measurements cover the period from 16/09/2007 to 09/09/2008. Salinity and temperature were logged every 15 min at 3 metres above the seafloor with an SBE-16 CT sensor. Two Seapoint optical backscatter sensors were fitted to the lander at 1 and 3 metres above the seafloor recording data every 15 min. Biofouling of the sensor windows may have affected the results, and the lowest sensor (1 mab) appeared temporarily saturated by high turbidity. Full details about the deployment can be found in Jonkers et al., 2010 (doi:10.1016/j.dsr.2010.05.005).

Description: To monitor particle fluxes and near bottom hydrographic variability a modified version of the benthic Bottom Boundary (BOBO) lander was deployed at 57 29.09 N, 27 54.53 W on the Gardar Drift at a water depth of 2630 m. The lander was fitted with three extended Technicap PPS 4/3 sediment traps, each with a baffled collecting area of 0.05 m2 positioned at 4 metres above the seafloor. Trap bottles were filled with ambient seawater and poisoned with a pH-buffered HgCl2 solution and rotated every 11 days. To test the performance of each sediment trap, two traps were programmed to collect material synchronously for three intervals during the deployment. Fluxes were intercepted successfully from 2007-09-19 through 2008-08-03. Full details about the deployment can be found in Jonkers et al., 2010 (doi:10.1016/j.dsr.2010.05.005). Pitch and roll of the lander were recorded and displayed very little variation (1.8370.031 and 0.3370.041, respectively); trapping efficiency was thus uncompromised by the movement of the lander. Upon recovery the pH of the supernatant was measured and found to range from 8.5 to 8.8, indicating minimum sample degradation. The samples were stored at 4 degC. Before sample processing in the laboratory the supernatant was sampled for dissolved Si analysis to correct for the dissolution of the particulate biogenic silica (doi:10.1016/j.margeo.2005.11.001; doi:10.1016/S0967-0645(97)00018-0). Swimmers larger than 1 mm were removed prior to splitting of the samples for further analysis. Carbon and nitrogen were separately analysed on weighed aliquots of the bulk material before and after removal of the carbonate-carbon (doi:10.1016/S0967-0637(02)00030-4) using a Carlo Erba Instruments Flash 1112 elemental analyzer. Biogenic silica (BSi) was determined by continuous alkaline leaching that accounts for contributions by co-leaching of Al-silicates (doi:10.1023/A:1020318610178). The lithogenic content was calculated according to doi:10.1016/S0924-7963(02)00189-6. Samples were analysed for 210Pb activity using the granddaughter 210Po by means of spectrometry. About 10 mg of trap material was spiked with 209Po and leached with concentrated HCl. Polonium isotopes were collected onto silver disks and counted for at least two days with Canberra alpha detectors.

Description: We present an almost 3 year long time series of shell fluxes and oxygen isotopes of left-coiling Neogloboquadrina pachyderma and Turborotalita quinqueloba from sediment traps moored in the deep central Irminger Sea. We determined their response to the seasonal change from a deeply mixed water column with occasional deep convection in winter to a thermally stratified water column with a surface mixed layer (SML) of around 50 m in summer. Both species display very low fluxes during winter with a remnant summer population holding out until replaced by a vital population that seeds the subsequent blooms. This annual population overturning is marked by a 0.7 per mill increase in d18O in both species. The shell flux of N. pachyderma peaks during the spring bloom and in late summer, when stratification is close to its minimum and maximum, respectively. Both export periods contribute about equally and account for 〉95% of the total annual flux. Shell fluxes of T. quinqueloba show only a single broad pulse in summer, thus following the seasonal stratification cycle. The d18O of N. pachyderma reflects temperatures just below the base of the seasonal SML without offset from isotopic equilibrium. The d18O pattern of T. quinqueloba shows a nearly identical amplitude and correlates highly with the d18O of N. pachyderma. Therefore T. quinqueloba also reflects temperature near the base of the SML but with a positive offset from isotopic equilibrium. These offsets contrast with observations elsewhere and suggest a variable offset from equilibrium calcification for both species. In the Irminger Sea the species consistently show a contrast in their flux timings. Their flux-weighted delta d18O will thus dominantly be determined by seasonal temperature differences at the base of the SML rather than by differences in their depth habitat. Consequently, their sedimentary delta d18O may be used to infer the seasonal contrast in temperature at the base of the SML.

Description: Measurement were conducted using a NewWave UP193 solid-state laser coupled to a Thermo‐Finnigan Element2 HR-ICP-MS at the Department of Geosciences, University of Bremen. Isotope abundances of 25Mg, 27Al, 43Ca, 55Mn, 57Fe and 87Sr in foraminifera shells were determined at an irradiance of 1.3 GW cm-2, a laser pulse rate of 5 Hz and a spot size of 50–100 μm. Plasma power was 1200 W, and Helium (0.7 L min-1) and Argon (0.9 L min-1) were used as sample and make-up gases, respectively. All isotopes were analysed at low resolution with five samples in a 20% mass window and a total dwell time of 25 ms per isotope. Blanks were measured for 30 s prior to ablation and every analysis was followed by a wash out time of at least 60 s to avoid cross-contamination between samples. A glass reference material (NIST610) was measured before every five ablation spots as an external calibration standard using the values of Jochum et al. (2011). To assess data quality, a pressed pellet of MACS-3 carbonate standard powder (n=4) and the USGS reference material BHVO‐2G (n=18) were analysed as control standards along with the samples. External precision is better than 3.9%, and accuracy as determined by comparison of our reference material data with the GeoReM database (as of July 2020) is better than 3.4% for all elements except for Mg (7.7%). The 43Ca isotope was used as an internal standard. The files contain raw and despiked element counts, calibration factors and calibrated element/calcium ratios.

Description: Previous work showed that South Atlantic sediments have lower glacial than Holocene 231Pa/230Th, which was attributed to a switch in the flow direction of Atlantic deep-water. Debate exists, however as to the degree to which two processes - circulation and scavenging - determine sedimentary 231Pa/230Th, making this interpretation contentious. Here we address this issue using 145-kyr records of paleocirculation proxies. Benthic foraminiferal d13C, neodymium isotopes (ENd) and sedimentary 231Pa/230Th were all measured in a single sediment core from the South Atlantic subtropical gyre. This site largely excludes the influence of local productivity changes on 231Pa/230Th records. Measured 231Pa/230Th ranges between ~0.041 during glacials to ~0.055 during interglacial periods and are consistently lower than the production ratio, indicating export of 231Pa from the central South Atlantic for the entire duration of the record. The lower glacial 231Pa/230Th is regionally consistent, suggesting that basin-scale oceanographic processes cause the decrease. In turn, less radiogenic ENd and lower benthic d13C confirm the classical picture of an increase in Southern Component Water (SCW) influence in the Atlantic during glacial periods and point to a circulation control on the observed 231Pa/230Th decrease rather than a local productivity change. We suggest that associated with this change in water mass distribution the dominant sink for 231Pa shifted from the margins of the South Atlantic and/or the Southern Ocean during interglacials, to the North Atlantic during glacial periods. Indeed, elevated 231Pa/230Th in the deep North Atlantic during glacials supports this mechanism of northward transport of 231Pa by SCW.