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>

The eastern Mediterranean pre-MSC brine pool as an analogue for future subtropical hydroclimate

2021 ◽  
Author(s):  
George Kontakiotis ◽  
Geanina Butiseaca ◽  
Assimina Antonarakou ◽  
Vasileios Karakitsios ◽  
Stergios D. Zarkogiannis ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
Water Column ◽  
Sea Level ◽  
Eastern Mediterranean ◽  
Sea Surface ◽  
Sea Surface Salinity ◽  
Time Interval ◽  
Surface Salinity ◽  
The Mediterranean ◽  
Brine Pool

<p>During the Late Miocene the Mediterranean Sea experienced severe disruption of its connectivity to the Atlantic Ocean, highlighted by a rapid sea-level drop, culminating to the Messinian Salinity Crisis (MSC; 5.97-5.33 Ma). Such a paleoceanographic change, triggered by the cumulative effect of climate and tectonics, caused high-amplitude fluctuations in the hydrology of the entire basin, and further influenced the geological history of the Mediterranean Sea. Although a consistent pattern of the paleoclimate has started to emerge, we currently lack a continuous sea surface salinity (SSS) record linking the timing of sea surface temperature (SST) variations, sea-level fluctuations, and the overall environmental change, particularly for the pre-evaporitic period. Initial viewpoints of a linear and gradual salinity increase prior to the onset of the MSC have been recently revised and replaced by highly variable salinity-related patterns representative of the stepwise restriction of the Mediterranean Sea. Here we use the combined Tetra Ether (TEX<sub>86</sub>-) and/or alkenone unsaturation ratio (U<sup>K′</sup><sub>37</sub>) based SSTs and oxygen isotopes (δ<sup>18</sup>O) from the cyclic marl-sapropel sedimentary succession of Agios Myron section (north-central Crete, Greece) to assess hydroclimate changes during that time, and we finally present the first record of SSS in the eastern Mediterranean Sea for the earliest Messinian (7.2–6.5 Ma). The relatively stable marine conditions after the Tortonian/Messinian boundary, expressed through a cool and fresh upper water column, significantly changed at ∼6.9 Ma, when an important reversal in the heart of the Messinian cooling trend supplemented by a coherent hypersaline water column took place. The observed SST and SSS patterns provide context for a two-fold evolution of this event (centered at 6.9–6.8 and 6.72 Ma), which finally led to the onset of a brine pool into the eastern Mediterranean basin. The transitional character of the following time interval (6.7–6.5 Ma) marks another important step in the basin restriction with a wider range of salinity fluctuations from highly saline to diluted conditions and enhanced water column stratification prior to the deposition of evaporites. Overall, this evolution supports the concept of a stepwise restriction of the Mediterranean Sea associated with substantial hydroclimate variability and increasing environmental (thermal and salinity) stress, and further confirms its position as a preferred laboratory for developing new conceptual models in paleoceanography, allowing the investigation and scale assessment of a phenomenon with high chances of representing a future analogue scenario.</p>

Seawater temperature, productivity and marine fish metabolism in the Messinian eastern Mediterranean

2021 ◽  
Author(s):  
Konstantina Agiadi ◽  
Danae Thivaiou ◽  
Geanina Butiseaca ◽  
George Kontakiotis ◽  
Eva Besiou ◽  
...  
Keyword(s):  
Surface Water ◽  
Water Column ◽  
Bottom Water ◽  
Eastern Mediterranean ◽  
Sea Surface ◽  
Isotopic Ratios ◽  
Bottom Water Temperature ◽  
Crete Island ◽  
Water Conditions ◽  
Stable Oxygen

<p>Reconstructing paleoceanographic conditions for the entire water column remains challenging, due to the lack of proxies for seawater parameters below surface waters, which could be used to validate models. Fish otoliths and ostracods are used here to obtain biogeochemical proxy data of sea surface/bottom temperature and productivity, as well as the biological response of marine fishes to paleoenvironmental change. Our study area is located in the eastern Mediterranean Sea (Heraklion basin, Crete Island). During the Messinian age (specifically between 7.2 and 6.5 Ma), the Mediterranean–Atlantic connection was restricted leading to a strongly stratified water column. We study the sea surface and bottom conditions under these conditions.</p><p>Stable oxygen isotopes on ostracod valves (<em>Bairdoppilata </em>sp.) reflect the combined effect of bottom-water temperature and salinity changes. For fishes however, this depends on each species lifestyle. We analyzed two very common species: 1) <em>Bregmaceros albyi</em>, a surface-water pelagic species, and 2) <em>Lesueurigobius friesii</em>, a demersal fish dwelling on the sea bottom. Our hypothesis was that the stable oxygen isotopic ratios on <em>B. albyi</em> otoliths would reflect surface-water conditions, whereas those on <em>L. friesii </em>would correspond to bottom-water conditions. Furthermore, we obtained δ<sup>13</sup>C values for the same ostracod and otolith specimens. Stable carbon isotopic ratios in invertebrate shells indicate biological productivity, since carbon fractionation takes place as a single-step process during biomineralization. However, fish otolith aragonite mineralization is more complicated, involving more than one fractionation steps, and carbon is obtained from seawater, but also from diet. Therefore,  otolith δ<sup>13</sup>C is considered a proxy of the fish’s field metabolic rate, reflecting its ability to continue to grow and reproduce despite environmental change.</p><p>Our results show that <em>B. albyi</em> δ<sup>18</sup>O values correlate well with those derived from planktonic foraminifera shells, whereas <em>L. friesii</em> δ<sup>18</sup>O is in agreement with ostracod values, thereby confirming our hypothesis. Moreover, ostracod and foraminifera δ<sup>13</sup>C follow the same decreasing pattern. However, otolith δ<sup>13</sup>C remains stable, even after 6.8 Ma, when high-amplitude salinity variations prevail. This suggests that fish maintained their capacity to grow and reproduce despite significant changes in seawater conditions at least until 6.5 Ma. However, whether this reflects their resilience to these environmental changes or an adaptation mechanism such as reducing their growth rate or shifting their trophic preferences remains a mystery.</p>

scholarly journals Microbial community genomics in eastern Mediterranean Sea surface waters

2009 ◽  
Vol 4 (1) ◽  
pp. 78-87 ◽  
Author(s):  
Roi Feingersch ◽  
Marcelino T Suzuki ◽  
Michael Shmoish ◽  
Itai Sharon ◽  
Gazalah Sabehi ◽  
...  
Keyword(s):  
Microbial Community ◽  
Mediterranean Sea ◽  
Surface Waters ◽  
Eastern Mediterranean ◽  
Sea Surface ◽  
Eastern Mediterranean Sea

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.

scholarly journals Integrated survey of elemental stoichiometry (C, N, P) from the Western to Eastern Mediterranean Sea

2010 ◽  
Vol 7 (5) ◽  
pp. 7315-7358 ◽  
Author(s):  
M. Pujo-Pay ◽  
P. Conan ◽  
L. Oriol ◽  
V. Cornet-Barthaux ◽  
C. Falco ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
Water Column ◽  
Surface Waters ◽  
Eastern Mediterranean ◽  
Vertical Gradient ◽  
Western Basin ◽  
P Limitation ◽  
Severe Deficiency ◽  
Elemental Stoichiometry ◽  
Redfield Ratios

Abstract. This paper provides an extensive vertical and longitudinal description of the biogeochemistry in the whole Mediterranean Sea during the summer 2008. During this strong stratified period, the distribution of nutrients, particulate and dissolved organic carbon (DOC), nitrogen (DON) and phosphorus (DOP) were investigated along a 3000 km transect (BOUM cruise) crossing the Western and Eastern Mediterranean basins. The partitioning of chemical C, N and P species among all these mineral and organic pools has been analysed to produce a detailed spatial and vertical extended examination of the elemental stoichiometry. Surface Mediterranean waters were depleted in nutrients and the thickness of this depleted layer increased towards the East from about 10 m in the Gulf of Lion to more than 100 m in the Levantine basin, concomitantly to the gradual deepening of the thermocline and nutriclines. We used threshold in oxygen concentration to discriminate the water column in three layers; surface (Biogenic Layer BL), intermediate (Mineralization Layer ML), and deep layer (DL) and to propose a schematic representation of biogeochemical fluxes between the different compartments and to compare the functioning of the two basins. The stoichiometry revealed a clear longitudinal and vertical gradient in the mineral fraction with a P-depletion evidenced on both dimension. As a consequence of the severe deficiency in phosphorus, the C:N:P ratios in all pools within the BL largely exceed the Redfield ratios. Despite these gradients, the deep estimated fluxes in the mineral compartment tend towards the canonical Redfield values in both basins. A change in particulate matter composition has been evidenced by a C increase relative to N and P along the whole water column in the western basin and between BL and ML in the eastern one. More surprisingly, a decrease in N relative to P with depth was encountered in the whole Mediterranean Sea. We suggest that there was a more rapid recycling of N than P in intermediate waters (below BL) and a complete use of DOP in surface waters. DOC accumulated in surface waters according to the oligotrophic status but this was not the case for nitrogen nor phosphorus. Our data clearly showed a noticeable stability of the DOC:DON ratio (12–13) in the whole Mediterranean Sea, contradicting the fact that N is recycled faster than C in the DOM but in agreement with a P limitation of bacterial activity. Finally, comparisons between these elemental distributions and ratios along the West-East Mediterranean gradient of trophic status provide new insights for identifying and understanding fundamental interactions between marine biogeochemistry and ecosystems, which will help to predict the impacts of environmental climate changes on the Mediterranean marine ecosystems. Indeed, the outflowing through the various Mediterranean straits have been shown to be changing, the functioning of the BL ecosystem could be impacted, not only by changes in nutrients surface sources but also by changes in deep nutrients one.

scholarly journals THE APPLICATION OF CYCLOSTRATIGRAPHY AND ASTROCHRONOLOGY IN THE NEOGENE MARINE DEPOSITS OF EASTERN MEDITERRANEAN: METOCHIA SECTION (GAVDOS ISLAND)

2006 ◽  
Vol 39 (1) ◽  
pp. 17
Author(s):  
A. Antonarakou ◽  
H. Drinia ◽  
F. Pomoni-Papaioannou
Keyword(s):  
Eastern Mediterranean ◽  
Climatic Changes ◽  
Sea Surface ◽  
Time Interval ◽  
Short Term ◽  
Solar Insolation ◽  
Marine Deposits ◽  
Long Term Trend

Significant lithostratigraphical and micropaleontological signatures, of Milankovitchscale climatic changes are recorded in Miocene deep-sea sediments. As a case study, the Metochia Section, in Gavdos Island, which covers the time interval from 9.7 to 6.6 Ma, is used. This study emphasizes the sedimentological and micropaleontological characteristics of the section, attributed to Milankovitch-scale climatic changes. The short-term variations in climate and faunal composition are related to precession- controlled sedimentary cycles and the long-term trend in climate is related to eccentricity and obliquity cycles. Regional changes in sea surface temperature in combination with variations of solar insolation have caused the cyclical astronomical controlled pattern of Globorotalia species.

scholarly journals Light absorption and partitioning in Arctic Ocean surface waters: impact of multi year ice melting

2013 ◽  
Vol 10 (3) ◽  
pp. 5619-5670 ◽  
Author(s):  
S. Bélanger ◽  
S. A. Cizmeli ◽  
J. Ehn ◽  
A. Matsuoka ◽  
D. Doxaran ◽  
...  
Keyword(s):  
Arctic Ocean ◽  
Water Column ◽  
Surface Waters ◽  
Sea Surface ◽  
The Arctic ◽  
Radiative Energy ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Ice Melting ◽  
The Impact

Abstract. Ice melting in the Arctic Ocean exposes the surface water to more radiative energy with poorly understood effects on photo-biogeochemical processes and heat deposition in the upper ocean. In August 2009, we documented the vertical variability of light absorbing components at 37 stations located in the southeastern Beaufort Sea including both Mackenzie river-influenced waters and polar mixed layer waters. We found that melting multi-year ice released significant amount of non-algal particulates (NAP) near the sea surface relative to sub-surface waters. NAP absorption coefficients at 440 nm (aNAP(440)) immediately below the sea surface (0-) were on average 3-fold (up to 10-fold) higher compared to sub-surface values measured at 2–3 m depth. The impact of this unusual feature on the light transmission and remote sensing reflectance (Rrs) was further examined using a radiative transfer model. A 10-fold particle enrichment homogeneously distributed in the first meter of the water column slightly reduced photosynthetically available and usable radiation (PAR and PUR) by ~6% and ~8%, respectively, relative to a fully homogenous water column with low particles concentration. In terms of Rrs, the particle enrichment significantly flattered the spectrum by reducing the Rrs by up to 20% in the blue-green spectral region (400–550 nm). These results highlight the impact of melt water on the concentration of particles at sea surface, and the need for considering nonuniform vertical distribution of particles in such systems when interpreting remotely sensed ocean color. Spectral slope of aNAP spectra calculated in the UV domain decreased with depth suggesting that this parameter is sensitive to detritus composition and/or diagenesis state (e.g., POM photobleaching).

Late Miocene sea surface salinity variability and paleoclimate conditions in the Eastern Mediterranean inferred from coral aragonite δ18O

2009 ◽  
Vol 262 (3-4) ◽  
pp. 202-216 ◽  
Author(s):  
R. Mertz-Kraus ◽  
T.C. Brachert ◽  
M. Reuter ◽  
S.J.G. Galer ◽  
C. Fassoulas ◽  
...  
Keyword(s):  
Late Miocene ◽  
Eastern Mediterranean ◽  
Sea Surface ◽  
Sea Surface Salinity ◽  
Surface Salinity ◽  
Salinity Variability

Air-Sea seasonal CO2 fluxes in a fast warming oligotrophic region – the Eastern Mediterranean case study

2020 ◽  
Author(s):  
Juntao Yu
Keyword(s):  
Mediterranean Sea ◽  
Surface Waters ◽  
Seasonal Variations ◽  
Eastern Mediterranean ◽  
Open Water ◽  
Sea Surface ◽  
Total Alkalinity ◽  
Eastern Region ◽  
Underlying Assumption ◽  
The Mediterranean

<p>In a recent study, it was suggested based on the apparent correlation between multi-annual measurements of summertime maxima and wintertime minima temperature and calculated pCO<sub>2</sub> in the most eastern region of the Mediterranean Sea surface waters that they are a net source of atmospheric CO<sub>2</sub>. Furthermore, it was predicted that the magnitude of this source would increase substantially in this region and that adjacent regions in the Eastern Mediterranean as well would turn into net sources of atmospheric CO<sub>2</sub> due to the fast warming of these waters. In order to confirm the underlying assumption that seasonal variations in pCO<sub>2</sub> in Eastern Mediterranean surface waters are primarily a strong function of seasonal variations in temperature, water samples were collected for the analysis of total alkalinity and pH during 12 monthly cruises from February 2018 to January 2019 at the shallow (THEMO1) and the deep (THEMO2) open water stations that are ca.10 and 20 NM off the Mediterranean coast of Israel. The data from all the cruises show that surface (< 30m depth) seawater pCO<sub>2</sub> has a strong positive linear relationship with temperature in both stations (n=56, r<sup>2</sup>=0.94, p<0.001). The calculated annual net flux of CO<sub>2</sub> from the surface to the atmosphere based on these measurements is ca.1.13 Tg C y<sup>−1</sup>, which is ca.15% higher than the previously estimated flux, but within its range of uncertainty (± 30%). These results clearly demonstrate that surface water pCO<sub>2</sub> levels are indeed a strong positive function of the seasonal variations in sea-surface temperature and that the open water of the most eastern Mediterranean Sea is a net source of atmospheric CO<sub>2</sub>. These results are also in agreement with the conclusions of observational and modelling studies of air-sea CO<sub>2</sub> fluxes in the centers of subtropical gyres and therefore globally relevant.</p>

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