Organic carbon losses measured by heterotrophic activity of mesozooplankton and CaCO3 flux in the bathypelagic zone of the Arabian Sea

Organic carbon requirements for metabolisms of mesozooplankton in the bathypelagic zone were calculated for two stations (Western Arabian Sea Sediment Trap, WAST, 16°N 60°E, and Central Arabian Sea Sediment Trap, CAST, 14°N 64°E) and two different intermonsoonal periods (October 1995 and April 1997) in the Arabian Sea. These requirements were compared with inputs of particulate organic carbon (POC) measured from sediment traps. The temporal variability of POC flux is compared to the CaCO3 flux made up by planktic foraminiferans and coccolithophorids. The potential oxygen requirement of mesozooplankton was measured by the electron transport system (ETS) activity and the organic carbon demand calculated using conversion factors from the literature. Particulate CaCO3 flux was calculated from multinet hauls and sediment trap samples. Mesozooplankton organic carbon demand in the zone between 1050 and 3000 m differed locally and seasonally. At WAST, the mesozooplankton required 1778 μg C m−2 d−1 in October and only 484 μg C m−2 d−1 in April. At CAST, the respective values were 997 and 211 μg C m−2 d−1. No differences between the stations and time periods were discernible for the zone between 3000 and 3900 m at CAST and between 3000 and 4000 m at WAST; the values ranged between 73 and 98 μg C m−2 d−1. The input measured by sediment traps was sufficient to cover the calculated requirements of the mesozooplankton. The flux of calcareous particles and the mesozooplankton carbon requirements showed a similar pattern of temporal variability. At CAST the planktic foraminiferal shell flux was 33.2 mg CaCO3 m−2 d−1 in October and only 5.9 mg CaCO3 m−2 d−1 at 3000 m depth in April. Flux data derived from multinet hauls are of the same order of magnitude as the sediment trap data and, as multinet data yield a high temporal and spatial resolution, they could serve as a measure for open-ocean particulate flux

Planktic foraminiferal changes in the western Mediterranean Anthropocene

Unidad de excelencia María de Maeztu CEX2019-000940-MAltres ajuts: Acord transformatiu CRUE-CSICThe increase in anthropogenic induced warming over the last two centuries is impacting marine environment. Planktic foraminifera are a globally distributed calcifying marine zooplankton responding sensitively to changes in sea surface temperatures and interacting with the food web structure. Here, we study two high resolution multicore records from two western Mediterranean Sea regions (Alboran and Balearic basins), areas highly affected by both natural climate change and anthropogenic warming. Cores cover the time interval from the Medieval Climate Anomaly to present. Reconstructed sea surface temperatures are in good agreement with other results, tracing temperature changes through the Common Era (CE) and show a clear warming emergence at about 1850 CE. Both cores show opposite abundance fluctuations of planktic foraminiferal species (Globigerina bulloides, Globorotalia inflata and Globorotalia truncatulinoides), a common group of marine calcifying zooplankton. The relative abundance changes of Globorotalia truncatulinoides plus Globorotalia inflata describe the intensity of deep winter mixing in the Balearic basin. In the Alboran Sea, Globigerina bulloides and Globorotalia inflata instead respond to local upwelling dynamics. In the pre-industrial era, changes in planktic foraminiferal productivity and species composition can be explained mainly by the natural variability of the North Atlantic Oscillation, and, to a lesser extent, by the Atlantic Multidecadal Oscillation. In the industrial era, starting from about 1800 CE, this variability is affected by anthropogenic surface warming, leading to enhanced vertical stratification of the upper water column, and resulting in a decrease of surface productivity at both sites. We found that natural planktic foraminiferal population dynamics in the western Mediterranean is already altered by enhanced anthropogenic impact in the industrial era, suggesting that in this region natural cycles are being overprinted by human influences

The Purified E. coli Integral Membrane Protein SecY/E Is Sufficient for Reconstitution of SecA-Dependent Precursor Protein Translocation

We have previously reconstituted the soluble phase of precursor protein translocation in vitro using purified proteins (the precursor proOmpA, the chaperone SecB, and the ATPase SecA) in addition to isolated inner membrane vesicles. We now report the isolation of the SecY/E protein, the integral membrane protein component of the E. coli preprotein translocase. The SecY/E protein, reconstituted into proteoliposomes, acts together with SecA protein to support translocation of proOmpA, the precursor form of outer membrane protein A. This translocation requires ATP and is strongly stimulated by the protonmotive force. The initial rates and the extents of translocation into either native membrane vesicles or proteoliposomes with pure SecY/E are comparable. The SecY/E protein consists of SecY, SecE, and an additional polypeptide. Antiserum against SecY immunoprecipitates all three components of the SecY/E protein

Low planktic foraminiferal diversity and abundance observed in a spring 2013 west-east Mediterranean Sea plankton tow transect

Unidad de excelencia María de Maeztu MdM-2015-0552Planktic foraminifera were collected with 150 µm BONGO nets from the upper 200 m water depth at 20 stations across the Mediterranean Sea between 2 May and 2 June 2013. The main aim is to characterize the species distribution and test the covariance between foraminiferal area density (ρA) and seawater carbonate chemistry in a biogeochemical gradient including ultraoligotrophic conditions. Average foraminifera abundances are 1.42 ± 1.43 ind. 10 m⁻³ (ranging from 0.11 to 5.20 ind. 10 m⁻³), including 12 morphospecies. Large differences in species assemblages and total abundances are observed between the different Mediterranean sub-basins, with an overall dominance of spinose, symbiont-bearing species indicating oligotrophic conditions. The highest values in absolute abundance are found in the Strait of Gibraltar and the Alboran Sea. The western basin is dominated by Globorotalia inflata and Globigerina bulloides at slightly lower standing stocks than in the eastern basin. In contrast, the planktic foraminiferal assemblage in the warmer, saltier, and more nutrient-limited eastern basin is dominated by Globigerinoides ruber (white). These new results, when combined with previous findings, suggest that temperature-induced surface water stratification and food availability are the main factors controlling foraminiferal distribution. In the oligotrophic and highly alkaline and supersaturated with respect to calcite and aragonite Mediterranean surface water, standing stocks and ρA of G. ruber (white) and G. bulloides are affected by both food availability and seawater carbonate chemistry. Rapid warming increased surface ocean stratification impacting food availability and changes in trophic conditions could be the causes of reduced foraminiferal abundance, diversity, and species-specific changes in planktic foraminiferal calcification

High‐Resolution Mg/Ca Measurements of Foraminifer Shells Using Femtosecond LA‐ICP‐MS for Paleoclimate Proxy Development

Determination of Mg/Ca in foraminifer shells as a proxy of seawater temperature is of particular interest in paleoclimate reconstruction. Here we show that femtosecond–200 nm–laser ablation–inductively coupled plasma–mass spectrometry is a suitable technique to precisely and accurately determine Mg/Ca in the micrometer-sized calcareous chambers of foraminifers. At low fluence (0.3–0.6 J/cm 2 ) the double-charged 44 Ca ++ and the single-charged 25 Mg + ions are measured nearly simultaneously. Integrated single-shot measurements using a pulse repetition rate of 1 Hz enable precise analyses at a depth resolution of about 50–100 nm/pulse corresponding to an ablated material of 0.3–0.6 ng calcite/pulse for a spot size of 55 μm. High-resolution analyses can be performed until a depth of 10–20 μm and thus particularly suitable for thin-shelled foraminifers. Reproducibility (relative standard deviation) is about 5% as approved by homogeneous reference materials. Calibration is performed with the microanalytical synthetic reference material MACS-3. Magnesium and Ca data of different carbonate and silicate reference materials agree within uncertainties with reference values. The procedure has been successfully applied for detailed analyses of single chambers and shell-depth profiles of live individuals and empty planktic and benthic foraminifer tests from different ocean basins

High Precision Femtosecond Laser Ablation ICP‐MS Measurement of Benthic Foraminiferal Mn‐Incorporation for Paleoenvironmental Reconstruction: A Case Study From the Plio‐Pleistocene Caribbean Sea

Closure of the Central American Seaway (CAS) and hydrology of the Caribbean Sea triggered Northern Hemisphere Glaciation and played an important role in the Pliocene to modern-day climate re-establishing the deep and surface ocean currents. New data on Mn/Ca obtained with femtosecond laser ablation inductively coupled plasma mass spectrometry on well-preserved tests of the epibenthic foraminifer Cibicidoides wuellerstorfi and infaunal C. mundulus contribute to the interpretation of paleoenvironmental conditions of the Caribbean Sea between 5.2 and 2.2 Ma (million years) across the closure of the CAS. Hydrothermal activity at the Lesser Antilles may be a primary source of Mn in the well-oxygenated Plio-Pleistocene Caribbean Sea. Incorporation of Mn in the benthic foraminifer shell carbonate is assumed to be affected by surface ocean nutrient cycling, and may hence be an indicator of paleoproductivity. Key Points - Femtosecond-laser ablation inductively coupled plasma mass spectrometry provides a new approach on distinguishing Mn of the ontogenetic shell calcite from Mn of the authigenic coatings - Ontogenetic Mn within the foraminifer shell calcite may result from the regional nutrient cycle - Mn in the deep eastern Caribbean Sea may mainly derive from hydrothermal sources along the Antilles Island Ar

Holocene records in the southeastern Bay of Biscay: global versus regional climate signals

Core KS10b (North East Atlantic, water depth 550 m) was recovered at a location of high sediment deposition including a high-resolution palaeoclimatic record for the southeastern Bay of Biscay (BoB) over the last 9.0 cal ka BP. The effect of global and regional climatic forcing factors (e.g. orbital forcing, North Atlantic Oscillation: NAO) and their subsequent control on water temperature, sea-level, hydrology and continental influence were investigated by studying foraminiferal faunas, sedimentology, and stable isotopes. Results indicate probable episodic incursions of the warm and salty Iberian Poleward Current (IPC) into the BoB by the intermittent presence of the subtropical species Globigerinoides ruber. These incursions seem to be triggered by negative NAO-like conditions. Our data show five main climatic periods, which are in general agreement with literature data on the climatic variability in the North Atlantic and the Iberian Peninsula: The early Holocene (~9.0–7.4 cal ka BP) is characterised by low sea-level, significant downslope transport, eutrophic benthic settings and high surface water productivity. These environmental characteristics are probably due to the general wet and warm climate under a prevailing negative NAO, increasing precipitation and river runoff and favouring the incursion of the IPC into the BoB. The climatic optimum appears between ~7.4 and 6.0 cal ka BP under a generally positive NAO index. In the following (~6.0–3.5 cal ka BP), surface water cooling is matching a steep decline of the Northern Hemisphere summer insolation. Meanwhile, benthic settings are changing progressively towards present day trophic conditions. The time interval from ~3.5 to 1.8 cal ka BP encompasses the Iberian-Roman Humid period characterised by warm and humid conditions, and increasing primary production under a prevailing negative NAO index. The last 1.8 ka were characterised by stable cool conditions, reflecting a change towards a positive NAO state