scholarly journals Carbon isotope excursions during the late Miocene recorded by lipids of marine Thaumarchaeota, Piedmont Basin, Mediterranean Sea

Geology ◽  
2021 ◽  
Author(s):  
Mathia Sabino ◽  
Daniel Birgel ◽  
Marcello Natalicchio ◽  
Francesco Dela Pierre ◽  
Jörn Peckmann
Keyword(s):  
Carbon Cycle ◽  
Mediterranean Sea ◽  
Water Column ◽  
Late Miocene ◽  
Dissolved Inorganic Carbon ◽  
Proximal Part ◽  
Fractionation Factor ◽  
Water Column Stratification ◽  
Group I ◽  
Thermohaline Stratification

Group I mesophilic Thaumarchaeota fix dissolved inorganic carbon (DIC), accompanied by a biosynthetic fractionation factor of ~20‰. Accordingly, the δ13C signature of their diagnostic biomarker crenarchaeol was suggested as a potential δ13CDIC proxy in marine basins if input from nonmarine Thaumarchaeota is negligible. Semi-enclosed basins are sensitive to carbon-cycle perturbations, because they tend to develop thermohaline stratification. Water column stratification typified the semi-enclosed basins of the Mediterranean Sea during the late Miocene (Messinian) salinity crisis (5.97–5.33 Ma). To assess how the advent of the crisis affected the carbon cycle, we studied sediments of the Piedmont Basin (northwestern Italy), the northernmost Mediterranean subbasin. A potential bias of our δ13CDIC reconstructions from the input of soil Thaumarchaeota is discarded, since high and increasing branched and isoprenoid tetraether (BIT) index values do not correspond to low and decreasing δ13C values for thaumarchaeal lipids, which would be expected in case of high input from soil Thaumarchaeota. Before the onset of the crisis, the permanently stratified distal part of the basin hosted a water mass below the chemocline with a δ13CDIC value of approximately –3.5‰, while the well-mixed proximal part had a δ13CDIC value of approximately –0.8‰. The advent of the crisis was marked by 13C enrichment of the DIC pool, with positive δ13CDIC excursions up to +5‰ in the upper water column. Export of 12C to the seafloor after phytoplankton blooms and limited replenishment of remineralized carbon due to the stabilization of thermohaline stratification primarily caused such 13C enrichment of the DIC pool.

Climate and carbon cycle changes drive the hydrographic configuration of the eastern Mediterranean through the Tortonian-Messinian Transition

2021 ◽  
Author(s):  
Evangelia Besiou ◽  
George Kontakiotis ◽  
Assimina Antonarakou ◽  
Andreas Mulch ◽  
Iuliana Vasiliev
Keyword(s):  
Carbon Cycle ◽  
Water Column ◽  
Surface Waters ◽  
Late Miocene ◽  
Eastern Mediterranean ◽  
Sea Surface ◽  
Time Interval ◽  
Climate Modelling ◽  
Paleoenvironmental Reconstruction ◽  
Crete Island

<p>The Late Miocene has been considered one of the most climatically stable periods of the Cenozoic, time span characterized by minor long-term cooling and ice growth. Especially, the Tortonian-Messinian Transition is recognized as a priority for paleoenvironmental reconstruction and climate modelling due to the significant paleoenvironmental changes preceding the Messinian Salinity Crisis (MSC; 5.97-5.33 Ma). Here, we present stable oxygen (δ<sup>18</sup>O) and carbon (δ<sup>13</sup>C) isotopes measured on benthic and planktonic foraminifera from Potamida section (Crete Island, eastern Mediterranean). The δ<sup>18</sup>O results indicate a decoupling between the surface and the bottom water column starting before the Tortonian-Messinian boundary. The difference between planktonic and benthic oxygen isotope signals (Δδ<sup>18</sup>O) further provides an estimate of the degree of water column stratification during that time. The δ<sup>13</sup>C data indicate a generally trend towards lighter values as an excellent illustration of the Late Miocene Carbon Isotope Shift (LMCIS; 7.6-6.6 Ma) due to progressive restriction of the Mediterranean basin, with the exception of the 7.38-7.26 Ma time interval where significantly heavier δ<sup>13</sup>C values are documented in both records. Such changes in carbon cycle seem to be most pronounced in the planktonic foraminiferal record (surface waters) through a 6-cycle development indicative of a cyclic productivity pattern during the latest Tortonian. The entire record is substantiated by sea surface temperature (SST) estimates based on TEX<sub>86</sub> biomarker based proxy. The reconstructed SST record shows that a warm phase characterized the late Tortonian sea surface (~27⁰C), time followed by a strong, steady cooling starting with earliest Messinian, when the SSTs dropped to values as low as 20⁰C. The outcome of the combined stable isotope and biomarker based SST data hint to increased salinity in the surface waters already before the Messinian, while at the Tortonian-Messinian Transition, the conditions in the surface waters changed towards cooler (~24⁰C) and normal salinity conditions.</p>

scholarly journals Acidification, deoxygenation, nutrient and biomasses decline in a warming Mediterranean Sea

2021 ◽  
Author(s):  
Marco Reale ◽  
Gianpiero Cossarini ◽  
Paolo Lazzari ◽  
Tomas Lovato ◽  
Giorgio Bolzon ◽  
...  
Keyword(s):  
Primary Production ◽  
Mediterranean Sea ◽  
Water Column ◽  
21St Century ◽  
Dissolved Inorganic Carbon ◽  
Net Primary Production ◽  
Eastern Mediterranean ◽  
Marine Ecosystems ◽  
Global Ocean ◽  
Co2 Absorption

Abstract. The projected warming, nutrient decline, changes in net primary production, deoxygenation and acidification of the global ocean will dramatically affect marine ecosystems during the 21st century. Here we assess the climate change-related impacts in the marine ecosystems of the Mediterranean Sea in the middle and at the end of the 21st century using high-resolution projections of the physical and biogeochemical state of the basin under the Representative Concentration Pathways (RCPs) 4.5 and 8.5. The analysis shows significant changes in the dissolved nutrient content of the euphotic and intermediate layers of the basin, net primary production, phytoplankton respiration and carbon stock (including phytoplankton, zooplankton, bacterial biomass and particulate organic matter). The projections also show a uniform surface and subsurface reduction in the oxygen concentration driven by the warming of the water column and by the increase in respiration. Moreover, we observe an acidification in the upper water column, linked to the increase in the dissolved inorganic carbon content of the water column due to CO2 absorption from the atmosphere and the increase in respiration. The projected changes are stronger in the eastern Mediterranean due to the limited influence, in that part of the basin, of the exchanges in the Strait of Gibraltar.

scholarly journals The geochemical and isotopic carbon cycle in an urban pond in the City of Wroclaw

2018 ◽  
Vol 18 (1) ◽  
pp. 3-8
Author(s):  
Wojciech Drzewicki ◽  
Pola Kościukiewicz ◽  
Adriana Trojanowska-Olichwer
Keyword(s):  
Carbon Cycle ◽  
Water Column ◽  
Inorganic Carbon ◽  
Dissolved Inorganic Carbon ◽  
Main Tool ◽  
Aquatic Organisms ◽  
Heavy Isotope ◽  
Isotopic Analyses ◽  
Urban Pond ◽  
Dynamic Growth

AbstractThe aim of this study was a recognition of the carbon cycle in a small anthropogenic reservoir located in Wrocław (SW Poland). The research investigated the geochemical processes and isotopic interactions in the water column as well as those between the water column and the sediment. Moreover, an attempt was made to identify the sources of carbon in the studied water body. Observations of temporal and spatial (vertical and horizontal) geochemical trends were the subject of this research. Chemical and isotopic analyses were the main tool used in this study. A total of 49 samples of water, sediment and plants were prepared, with sampling carried out in the period from October 2015 to May 2017. Two periods: autumn and spring were chosen for the study. During the autumn cycle, smaller variations in the values of δ13C in DIC were found compared to the spring cycle. The enrichment of dissolved inorganic carbon (DIC) in the heavy isotope during the spring period was caused by the dynamic growth of microorganisms. The process of assimilative reduction of dissolved inorganic carbon by aquatic organisms, which use inorganic carbon in biochemical reactions, occurred in the reservoir. This process led to an enrichment of DIC in the 13C isotope. The analysis of the sedimentary organic carbon revealed a greater enrichment in the heavy isotope of carbon (by about 3‰) in April compared to May. This is due to the growth of microorganisms responsible for degradation of sedimentary organic matter and plant detritus. The sediment and the water column were shown to interact through the exchange of carbon.

234Th cycling in the upper water column of the northwestern Mediterranean Sea

1990 ◽  
Vol 3 (1-2) ◽  
pp. 25-33 ◽  
Author(s):  
S. Schmidt ◽  
J.L. Reyss ◽  
H.V. Nguyen ◽  
P. Buat-Ménard
Keyword(s):  
Mediterranean Sea ◽  
Water Column ◽  
Northwestern Mediterranean Sea ◽  
Northwestern Mediterranean

Biogeochemical and ecological features of sinking particulate matter in the deep Ionian Sea (E. Mediterranean) during a 10-year time series study: impacts of atmospheric and oceanographic variabilities on carbon production and sequestration

2021 ◽  
Author(s):  
Alexandra Gogou ◽  
Constantine Parinos ◽  
Spyros Stavrakakis ◽  
Emmanouil Proestakis ◽  
Maria Kanakidou ◽  
...  
Keyword(s):  
Particulate Matter ◽  
Organic Carbon ◽  
Carbon Cycle ◽  
Atmospheric Deposition ◽  
Water Column ◽  
Particulate Organic Carbon ◽  
Nutrient Dynamics ◽  
Ionian Sea ◽  
Ecological Features ◽  
The Impact

<p>Biotic and abiotic processes that form, alter, transport, and remineralize particulate organic carbon, silicon, calcium carbonate, and other minor and trace chemical species in the water column are central to the ocean’s ecological and biogeochemical functioning and of fundamental importance to the ocean carbon cycle. Sinking particulate matter is the major vehicle for exporting carbon from the sea surface to the deep sea. During its transit towards the sea floor, most particulate organic carbon (POC) is returned to inorganic form and redistributed in the water column. This redistribution determines the surface concentration of dissolved CO<sub>2</sub>, and hence the rate at which the ocean can absorb CO<sub>2</sub> from the atmosphere. The ability to predict quantitatively the depth profile of remineralization is therefore critical to deciphering the response of the global carbon cycle to natural and human-induced changes.</p><p>Aiming to investigate the significant biogeochemical and ecological features and provide new insights on the sources and cycles of sinking particulate matter, a mooring line of five sediment traps was deployed from 2006 to 2015 (with some gap periods) at 5 successive water column depths (700, 1200, 2000, 3200 and 4300 m) in the SE Ionian Sea, northeastern Mediterranean (‘NESTOR’ site). We have examined the long-term records of downward fluxes for Corg, N<sub>tot</sub>, δ<sup>13</sup>Corg and δ<sup>15</sup>N<sub>tot</sub>, along with the associated ballast minerals (opal, lithogenics and CaCO<sub>3</sub>), lipid biomarkers, Chl-a and PP rates, phytoplankton composition, nutrient dynamics and atmospheric deposition.  </p><p>The satellite-derived seasonal and interannual variability of phytoplankton metrics (biomass and phenology) and atmospheric deposition (meteorology and air masses origin) was examined for the period of the sediment trap experiment. Regarding the atmospheric deposition, synergistic opportunities using Earth Observation satellite lidar and radiometer systems are proposed (e.g. Cloud‐Aerosol Lidar with Orthogonal Polarization - CALIOP, Moderate Resolution Imaging Spectroradiometer - MODIS), aiming towards a four‐dimensional exploitation of atmospheric aerosol loading (e.g. Dust Optical Depth) in the study area.</p><p>Our main goals are to: i) develop a comprehensive knowledge of carbon fluxes and associated mineral ballast fluxes from the epipelagic to the mesopelagic and bathypelagic layers, ii) elucidate the mechanisms governing marine productivity and carbon export and sequestration to depth and iii) shed light on the impact of atmospheric forcing and deposition in respect to regional and large scale circulation patterns and climate variability and the prevailing oceanographic processes (internal variability).</p><p>Acknowledgments</p><p>We acknowledge support of this work by the Action ‘National Network on Climate Change and its Impacts – <strong>CLIMPACT</strong>’, funded by the Public Investment Program of Greece (GSRT, Ministry of Development and Investments).</p>

scholarly journals Sediment-water column fluxes of carbon, oxygen and nutrients in Bedford Basin, Nova Scotia, inferred from <sup>224</sup>Ra measurements

2013 ◽  
Vol 10 (1) ◽  
pp. 53-66 ◽  
Author(s):  
W. J. Burt ◽  
H. Thomas ◽  
K. Fennel ◽  
E. Horne
Keyword(s):  
Organic Matter ◽  
Nova Scotia ◽  
Water Column ◽  
Explicit Knowledge ◽  
Dissolved Inorganic Carbon ◽  
Chemical Constituents ◽  
Water Interface ◽  
Benthic Fluxes ◽  
Pore Waters ◽  
Overlying Water

Abstract. Exchanges between sediment pore waters and the overlying water column play a significant role in the chemical budgets of many important chemical constituents. Direct quantification of such benthic fluxes requires explicit knowledge of the sediment properties and biogeochemistry. Alternatively, changes in water-column properties near the sediment-water interface can be exploited to gain insight into the sediment biogeochemistry and benthic fluxes. Here, we apply a 1-D diffusive mixing model to near-bottom water-column profiles of 224Ra activity in order to yield vertical eddy diffusivities (KZ), based upon which we assess the diffusive exchange of dissolved inorganic carbon (DIC), nutrients and oxygen (O2), across the sediment-water interface in a coastal inlet, Bedford Basin, Nova Scotia, Canada. Numerical model results are consistent with the assumptions regarding a constant, single benthic source of 224Ra, the lack of mixing by advective processes, and a predominantly benthic source and sink of DIC and O2, respectively, with minimal water-column respiration in the deep waters of Bedford Basin. Near-bottom observations of DIC, O2 and nutrients provide flux ratios similar to Redfield values, suggesting that benthic respiration of primarily marine organic matter is the dominant driver. Furthermore, a relative deficit of nitrate in the observed flux ratios indicates that denitrification also plays a role in the oxidation of organic matter, although its occurrence was not strong enough to allow us to detect the corresponding AT fluxes out of the sediment. Finally, comparison with other carbon sources reveal the observed benthic DIC release as a significant contributor to the Bedford Basin carbon system.

scholarly journals Bacteriohopanepolyols record stratification, nitrogen fixation and other biogeochemical perturbations in Holocene sediments of the central Baltic Sea

2013 ◽  
Vol 10 (4) ◽  
pp. 2725-2735 ◽  
Author(s):  
M. Blumenberg ◽  
C. Berndmeyer ◽  
M. Moros ◽  
M. Muschalla ◽  
O. Schmale ◽  
...  
Keyword(s):  
Baltic Sea ◽  
Water Column ◽  
Stable Stratification ◽  
The Baltic Sea ◽  
Allochthonous Input ◽  
The North ◽  
Water Column Stratification ◽  
Gotland Deep ◽  
History Of ◽  
The Baltic

Abstract. The Baltic Sea, one of the world's largest brackish-marine basins, established after deglaciation of Scandinavia about 17 000 to 15 000 yr ago. In the changeable history of the Baltic Sea, the initial freshwater system was connected to the North Sea about 8000 yr ago and the modern brackish-marine setting (Littorina Sea) was established. Today, a relatively stable stratification has developed in the water column of the deep basins due to salinity differences. Stratification is only occasionally interrupted by mixing events, and it controls nutrient availability and growth of specifically adapted microorganisms and algae. We studied bacteriohopanepolyols (BHPs), lipids of specific bacterial groups, in a sediment core from the central Baltic Sea (Gotland Deep) and found considerable differences between the distinct stages of the Baltic Sea's history. Some individual BHP structures indicate contributions from as yet unknown redoxcline-specific bacteria (bacteriohopanetetrol isomer), methanotrophic bacteria (35-aminobacteriohopanetetrol), cyanobacteria (bacteriohopanetetrol cyclitol ether isomer) and from soil bacteria (adenosylhopane) through allochthonous input after the Littorina transgression, whereas the origin of other BHPs in the core has still to be identified. Notably high BHP abundances were observed in the deposits of the brackish-marine Littorina phase, particularly in laminated sediment layers. Because these sediments record periods of stable water column stratification, bacteria specifically adapted to these conditions may account for the high portions of BHPs. An additional and/or accompanying source may be nitrogen-fixing (cyano)bacteria, which is indicated by a positive correlation of BHP abundances with Corg and δ15N.

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