• European Marine Science
• 2018-2022close
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Long-term, multi-parameter monitoring database that covers physical, chemical, and biological water properties at several stations along a Levantine micro-estuary and its neighboring coastal sea. The data are divided into two separate databases: Monthly surveys of water properties along the estuary and Bi-weekly surveys of water properties at two marine stations.

Sediment data from the Bahamian Santaren carbonate drift reveal the variability of trans-Atlantic Saharan dust transport back to about 100 ka BP (MIS 5.3) and demonstrate that carbonate drifts are a valuable pelagic archive of aeolian dust flux. Carbonate drift bodies are common around tropical carbonate platforms. They represent large-scale accumulations of ocean-current transported material, which originates from the adjacent shallow-water carbonate factory as well as from pelagic production, i.e. periplatform ooze. Subordinately, there is a clay- to silt-size non-carbonate fraction, which typically amounts to less than 10 % of the sediment volume and originates from aeolian and fluvial input. Sedimentation rates in the 5.42 m long core GeoHH-M95-524 recovered 25 km west of Great Bahama Bank in the Santaren Channel ranges from 1.5 to 24.5 cm ka-1 with lowest values during the last glacial lowstand and highest values following platform re-flooding around 8 ka BP. These sedimentation rates imply that carbonate drifts have not only the potential to resolve long-term environmental changes on orbital time scales, but also millennial to centennial fluctuations during interglacials. The sediment core has been investigated aiming on characterizing the lithogenic dust fraction. Laboratory analyses included XRF core scanning, determination of carbonate content, grain-size analyses (of bulk and terrigenous fraction), as well as visual inspections of the lithogenic residue; the age model is based on oxygen isotopes and radiocarbon ages. Data show that the input of aeolian dust in the periplatform ooze as indicated by Ti/Al and Fe/Al element ratios abruptly increases at 57 ka BP, stays elevated during glacial times, and reaches a Holocene minimum around 6.5 ka BP, contemporary to the African Humid Period. Subsequently, there is a gradual increase in dust flux which almost reaches glacial levels during the last centuries. Grain-size data show that the majority of dust particles fall into the fine silt range (below 10 µm); however, there is a pronounced coarse dust fraction in the size range up to 63 µm and individual 'giant' dust particles are up to 515 µm large. Total dust flux and the relative amounts of fine and coarse dust are decoupled. The time-variable composition of the grain-size spectrum is interpreted to reflect different dust transport mechanisms: fine dust particles are delivered by the trade winds and the geostrophic winds of the Saharan Air Layer, whereas coarse dust particles travel with convective storm systems. This mode of transport ensures continuous re-suspension of large particles and results in a prolonged transport. In this context, grain-size data from the terrigenous fraction of carbonate drifts provide a measure for past coarse dust transport, and consequently for the frequency of convective storm systems over the dust source areas and the tropical Atlantic.

The western tropical Atlantic plays an important role in the interhemispheric redistribution of heat during millennial-scale changes in the strength of the Atlantic Meridional Overturning Circulation (AMOC). The proper evaluation of this role depends on a clear understanding of sea surface temperature (SST) variations during AMOC slowdown periods like Heinrich Stadials (HS) in the western tropical Atlantic. However, published SST records from the western tropical Atlantic between ca. 4°S and 7°N show inconsistencies that are apparently related to the employed temperature proxy (i.e., Mg/Ca versus alkenone unsaturation index U37k′). In general, while Mg/Ca values indicate warming during Heinrich Stadials, U37k′ values show cooling. To assess this issue, we sampled core GeoB16224-1 retrieved off French Guiana (i.e., 6°39.38′N) and reconstructed water temperatures at high resolution using Mg/Ca on the foraminifera species Globigerinoides ruber, U37k′, TEX86 and modern analogue technique (MAT) transfer functions using planktonic foraminifera assemblages calibrated for 50 m water depth. Our results show that Mg/Ca and TEX86 values recorded an increase in SST related to AMOC slowdown. Conversely, U37k′ and MAT values registered a decrease in temperatures during HS3 and HS1. Our U37k′ and Mg/Ca results thus confirm the previously reported inconsistency for the period between 48-13 cal ka BP. We suggest that several non-thermal physiological effects probably imparted a negative temperature bias on the U37k′ temperatures during Heinrich Stadials. However, MAT-based temperatures show similar variability with U37k′-based temperatures. Hence, we also suggest that during severe slowdown periods of the AMOC, a steeper meridional temperature gradient together with a southward shift of the Intertropical Convergent Zone produced not only an increase in SST but also a stronger upper water column stratification and a shoaling of the thermocline, decreasing subsurface temperatures. Our new high resolution temperature records allow a better characterization of the thermal response of the upper water column in the tropical western Atlantic to slowdown events of the AMOC, reconciling previously discrepant records.

Most of the world's permafrost is located in the Arctic, where its frozen organic carbon con-tent makes it a potentially important influence on the global climate system. The Arctic climate appears to be changing more rapidly than the lower latitudes, but observational data density in the region is low. Permafrost thaw and carbon release into the atmosphere is a positive feed-back mechanism that has the potential for climate warming. It is therefore particularly im-portant to understand the links between the energy balance, which can vary rapidly over hour-ly to annual time scales, and permafrost condition, which changes slowly on decadal to cen-tennial timescales. This requires long-term observational data such as that available from the Samoylov research site in northern Siberia, where meteorological parameters, energy balance, and subsurface observations have been recorded since 1998. This paper presents the temporal data set produced between 2002 and 2017, explaining the instrumentation, calibration, pro-cessing and data quality control. Additional data include a high-resolution digital terrain mod-el (DTM) obtained from terrestrial LiDAR laser scanning. Since the data provide observations of temporally variable parameters that influence energy fluxes between permafrost, active lay-er soils, and the atmosphere (such as snow depth and soil moisture content), they are suitable for calibrating and quantifying the dynamics of permafrost as a component in earth system models. The data also include soil properties beneath different microtopographic features (a polygon center, a rim, a slope, and a trough), yielding much-needed information on landscape heterogeneity for use in land surface modeling. For the record from 1998 to 2017, the average mean annual air temperature was -12.3°C, with mean monthly temperature of the warmest month (July) recorded as 9.5°C and for the coldest month (February) -32.7°C. The average annual rainfall was 169mm. The depth of zero annual amplitude niveau is at 20.8m, and has warmed from -9.1°C in 2006 to -7.7°C in 2017.

Tropical and subtropical rivers deliver large quantities of terrestrial organic carbon to the ocean, acting as a crucial part of the global carbon cycle, but little is known about the timescale and efficiency of their transport to and in the adjacent coastal sea. Here, we examined source-specific biomarker (normal fatty acids (n-FAs)) contents and isotope compositions in surface sediments in an alongshore transect southwestward from the Pearl River mouth. The C~28+30~ rather than other long-chain n-FAs were found to be the most representative for OC~terr~, and a plant wax mean residence time (MRT) of 3060 ± 90 yr was estimated in the Pearl River watershed from the ¹⁴C age of C~28+30~ n-FA in the river mouth sample. A four-source mixing model demonstrated that the mean burial efficiency of fossil and soil OC is 85% and 49%, respectively, indicating the refractory nature of fossil OC but a significant loss of soil OC due to remineralization during transport in the marine environment before final burial. Thus, the remineralization of soil OC in the tropical coastal sea may be an important CO₂ source.

Attempts have been made to study the entire growth history of a manganese nodule from the northern part of Peru Basin in the Pacific using radiochemical profiles of 230Th232Th, 227Th230Th, and 10Be9Be. Combined with the observations on Fe-Mn contents and textural variation, the radiochemical data indicate that the nodule grew more or less concentrically throughout most of its existence since it formed 1.5 my ago, receiving Mn from both bottom water and pore water. This condition appeared to have changed about 180 ky ago when the growth became asymmetric in that the top and bottom sides became fixed in their relative positions on the sea floor. Since then, the bottom side accreted with a fast rate of close to 200 mm/my, apparently fueled by the supply of diagenetically remobilized Mn in pore water from the sediment substrate. In the meantime, the top side accumulated at about 6 mm/my, a value which is in the normal range for deep-sea nodules having their Mn supplied from the hydrogenous source.

Differences in habitat and diet between species are often associated with morphological differences. Habitat and trophic adaptation have therefore been proposed as important drivers of speciation and adaptive radiation. Importantly, habitat and diet shifts likely impose changes in exposure to different parasites and infection risk. As strong selective agents influencing survival and mate choice, parasites might play an important role in host diversification. We explore this possibility for the adaptive radiation of Lake Tanganyika (LT) cichlids. We first compare metazoan macroparasites infection levels between cichlid tribes. We then describe the cichlids' genetic diversity at the major histocompatibility complex (MHC), which plays a key role in vertebrate immunity. Finally, we evaluate to what extent trophic ecology and morphology explain variation in infection levels and MHC, accounting for phylogenetic relationships. We show that different cichlid tribes in LT feature partially non-overlapping parasite communities and partially non-overlapping MHC diversity. While morphology explained 15% of the variation in mean parasite abundance, trophic ecology accounted for 16% and 22% of the MHC variation at the nucleotide and at the amino acid level, respectively. Parasitism and immunogenetic adaptation may thus add additional dimensions to the LT cichlid radiation.

Much of our understanding of Earth's past climate states comes from the measurement of oxygen and carbon isotope variations in deep-sea benthic foraminifera. Yet, major intervals in those records that lack the temporal resolution and/or age control required to identify climate forcing and feedback mechanisms. Here we document 66 million years of global climate by a new high-fidelity Cenozoic global reference benthic carbon and oxygen isotope dataset (CENOGRID). Using recurrence analysis, we find that on timescales of millions of years Earth's climate can be grouped into Hothouse, Warmhouse, Coolhouse and Icehouse states separated by transitions related to changing greenhouse gas levels and the growth of polar ice sheets. Each Cenozoic climate state is paced by orbital cycles, but the response to radiative forcing is state dependent.

In permafrost areas, seasonal freeze-thaw cycles result in upward and downward movements of the ground. For some permafrost areas, long-term downward movements were reported during the last decade. We measured seasonal and multi-year ground movements in a yedoma region of the Lena River Delta, Siberia, in 2013–2017, using reference rods installed deep in the permafrost. The seasonal subsidence was 1.7 ± 1.5 cm in the cold summer of 2013 and 4.8 ± 2 cm in the warm summer of 2014. Furthermore, we measured a pronounced multi-year net subsidence of 9.3 ± 5.7 cm from spring 2013 to the end of summer 2017. Importantly, we observed a high spatial variability of subsidence of up to 6 cm across a sub-meter horizontal scale. In summer 2013, we accompanied our field measurements with Differential Synthetic Aperture Radar Interferometry (DInSAR) on repeat-pass TerraSAR-X (TSX) data from the summer of 2013 to detect summer thaw subsidence over the same study area. Interferometry was strongly affected by a fast phase coherence loss, atmospheric artifacts, and possibly the choice of reference point. A cumulative ground movement map, built from a continuous interferogram stack, did not reveal a subsidence on the upland but showed a distinct subsidence of up to 2 cm in most of the thermokarst basins. There, the spatial pattern of DInSAR-measured subsidence corresponded well with relative surface wetness identified with the near infra-red band of a high-resolution optical image. Our study suggests that (i) although X-band SAR has serious limitations for ground movement monitoring in permafrost landscapes, it can provide valuable information for specific environments like thermokarst basins, and (ii) due to the high sub-pixel spatial variability of ground movements, a validation scheme needs to be developed and implemented for future DInSAR studies in permafrost environments.

Radiocarbon ages measured on replicated samples, each sample containing a small (3-30) number of individual foraminifera picked from a discrete depth of a single sediment core. These data come from five sediment cores and were used to estimate the age-heterogeneity of material at discrete depths in the five cores. Radiocarbon ages made on larger "bulk" samples of foraminifera, or mean radiocarbon ages of multiple smaller samples. These were used to estimate sediment accumulation rates at the same four sediment cores.