Estimates of primary productivity have traditionally disregarded dark inorganic carbon fixation by marine microorganisms. Currently, only limited data are available from different systems on this ...potentially ecologically important process. We present monthly dark inorganic carbon fixation and photosynthetic rates from the euphotic layer of the northern Gulf of Aqaba collected over a decade between 2010 and 2020. Averaged dark inorganic carbon fixation rates from surface to 100 m depth, ranged from 99 to 173 mg C m−2 d−1, which corresponds to ~ 43% of the annual primary productivity at this location. The lowest dark inorganic carbon fixation rates were found during winter, contributing ~ 7.5% of the integrated primary productivity. During the oligotrophic summer, dark inorganic carbon fixation comprised a larger fraction of the integrated primary productivity estimated as ~ 12%. In accordance, dark inorganic carbon fixation contributed ~ 6% to the particulate organic carbon flux during the winter and ~ 30% during summertime. Complimentary nutrient‐enrichment bioassays of seawater from 5 m show that dissolved organic nutrient enrichment (P and C based) significantly elevates dark inorganic carbon fixation, whereas addition of dissolved inorganic nutrients (PO43+, NO3−, or both) significantly increased photosynthesis but to a lesser extent dark inorganic carbon fixation. These results suggest that dark inorganic carbon fixation may be an important biochemical process throughout the euphotic zone of oligotrophic seas, and thus should be incorporated into oceanic carbon production estimates.
The Mediterranean region is a climatic transitional zone between the subtropical/monsoon regime and the temperate westerlies and is subject to forces acting upon the global climate system. Much ...knowledge about its climate over the last millennium is derived from terrestrial records, whereas changes in sea surface temperatures (SSTs) and in the dissolved inorganic carbon pool (DIC) are poorly known. We present continuous high‐resolution reconstructions of SST and δ13CDIC in the eastern Mediterranean (EM) Sea, as inferred from oxygen and carbon isotope records from the skeletons of the reef builder gastropod Dendropoma sp. Spanning the past millennium, the SST reconstruction reveals a 250 year persistent warming trend during which the twentieth century was the warmest on record. Coupled with a distinct trend of 13CDIC depletion and superimposed upon decreased primary production, this climate reconstruction reflects a new state of the EM over the Anthropocene era that exceeds the natural variability of the last millennium.
Key Points
A new state of the EM over the Anthropocene
Persistent warming since 1750
Increasing oligotrophy is coupled with warming trend
Phytoplankton and heterotrophic bacteria rely on a suite of inorganic and organic macronutrients to satisfy their cellular needs. Here, we explored the effect of dissolved inorganic phosphate (PO
) ...and several dissolved organic molecules containing phosphorus ATP, glucose-6-phosphate, 2-aminoethylphosphonic acid, collectively referred to as dissolved organic phosphorus (DOP), on the activity and biomass of autotrophic and heterotrophic microbial populations in the coastal water of the southeastern Mediterranean Sea (SEMS) during summertime. To this end, surface waters were supplemented with PO
, one of the different organic molecules, or PO
+ ATP, and measured the PO
turnover time (Tt), alkaline phosphatase activity (APA), heterotrophic bacterial production (BP), primary production (PP), and the abundance of the different microbial components. Our results show that PO
alone does not stimulate any significant change in most of the autotrophic or heterotrophic bacterial variables tested. ATP addition (alone or with PO
) triggers the strongest increase in primary and bacterial productivity or biomass. Heterotrophic bacterial abundance and BP respond faster than phytoplankton (24 h post addition) to the various additions of DOP or PO
+ ATP, followed by a recovery of primary productivity (48 h post addition). These observations suggest that both autotrophic and heterotrophic microbial communities compete for labile organic molecules containing P, such as ATP, to satisfy their cellular needs. It also suggests that SEMS coastal water heterotrophic bacteria are likely C and P co-limited.
Past fish provenance, exploitation and trade patterns were studied by analyzing phosphate oxygen isotope compositions (δ
O
) of gilthead seabream (Sparus aurata) tooth enameloid from archaeological ...sites across the southern Levant, spanning the entire Holocene. We report the earliest evidence for extensive fish exploitation from the hypersaline Bardawil lagoon on Egypt's northern Sinai coast, as indicated by distinctively high δ
O
values, which became abundant in the southern Levant, both along the coast and further inland, at least from the Late Bronze Age (3,550-3,200 BP). A period of global, postglacial sea-level stabilization triggered the formation of the Bardawil lagoon, which was intensively exploited and supported a widespread fish trade. This represents the earliest roots of marine proto-aquaculture in Late Holocene coastal domains of the Mediterranean. We demonstrate the potential of large-scale δ
O
analysis of fish teeth to reveal cultural phenomena in antiquity, providing unprecedented insights into past trade patterns.
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•Long-term (∼40 y) record of deep-sea sharks denotes mercury accumulation.•Anthropogenic Hg accumulation is enhanced in oligotrophic deep-sea sharks.•Long-living deep-sea species show ...a temporal increase in THg levels.•THg is expected to further increase in deep marginal seas sharks.•Consumption of deep-sea sharks is potentially a high risk to human health.
Deep-sea habitats are currently recognized as a hot spot for mercury (Hg) accumulation from anthropogenic sources, resulting in elevated concentrations of total mercury (THg) in deep-sea megafauna. Among them, deep-sea sharks (Class Chondrichthyes) are characterized by high trophic position and extended longevity and are, therefore, at high risk for mercury contamination. Despite this, sharks are overexploited by fishing activity in increasingly deeper water, worldwide, imposing health risks to human consumption. While it is imperative to better understand long-term mercury contamination in deep-sea megafauna, few historical data sets exist to capture this process. Here we explore four decades (1985–2022) of THg accumulation in five species of deep-sea sharks (G. melastomus, E. spinax, S. rostratus, C. granulosus, and D. licha) of the ultra-oligotrophic Southeastern Mediterranean Sea (SEMS) sampled during 19 research cruises. We exhibited exceptionally high THg levels (per length/weight), the highest as 16.6 μg g−1 (wet wt.), almost entirely (98.9 %; n = 298 specimens) exceeding the limit for safe consumption (0.3–0.5 μg THg g−1 wet wt.). The maximal THg levels of the long-lived species D. licha and C. granulosus in the SEMS were enriched by a factor of ∼ 7 and >10 compared to counterpart species from other oceanic areas, respectively. We attribute this to the ultra-oligotrophic conditions of the SEMS, which cause slower growth rates and dwarfism in deep-sea sharks, resulting in an extended exposure time to mercury contamination. In the long-lived species, C. granulosus and D. licha, a temporal increase of average THg levels of ∼ 80 % was recorded between 1987–1999 and 2021–2022. This likely reflects the long-term accumulation of historical anthropogenic Hg in deep-sea environments, which is further amplified in marginal seas such as the Mediterranean, impacted by global air pollution crossroads and surrounded by land-based pollution sources. Future consumption of products from deep-sea sharks is potentially high risk to human health.
Abstract
The oceans play a major role in the earth’s climate by regulating atmospheric CO
2
. While oceanic primary productivity and organic carbon burial sequesters CO
2
from the atmosphere, ...precipitation of CaCO
3
in the sea returns CO
2
to the atmosphere. Abiotic CaCO
3
precipitation in the form of aragonite is potentially an important feedback mechanism for the global carbon cycle, but this process has not been fully quantified. In a sediment-trap study conducted in the southeastern Mediterranean Sea, one of the fastest warming and most oligotrophic regions in the ocean, we quantify for the first time the flux of inorganic aragonite in the water column. We show that this process is kinetically induced by the warming of surface water and prolonged stratification resulting in a high aragonite saturation state (Ω
Ar
≥ 4). Based on these relations, we estimate that abiotic aragonite calcification may account for 15 ± 3% of the previously reported CO
2
efflux from the sea surface to the atmosphere in the southeastern Mediterranean. Modelled predictions of sea surface temperature and Ω
Ar
suggest that this process may weaken in the future ocean, resulting in increased alkalinity and buffering capacity of atmospheric CO
2
.
Diet is a crucial trait of an animal's lifestyle and ecology. The trophic level of an organism indicates its functional position within an ecosystem and holds significance for its ecology and ...evolution. Here, we demonstrate the use of zinc isotopes (δ
Zn) to geochemically assess the trophic level in diverse extant and extinct sharks, including the Neogene megatooth shark (Otodus megalodon) and the great white shark (Carcharodon carcharias). We reveal that dietary δ
Zn signatures are preserved in fossil shark tooth enameloid over deep geologic time and are robust recorders of each species' trophic level. We observe significant δ
Zn differences among the Otodus and Carcharodon populations implying dietary shifts throughout the Neogene in both genera. Notably, Early Pliocene sympatric C. carcharias and O. megalodon appear to have occupied a similar mean trophic level, a finding that may hold clues to the extinction of the gigantic Neogene megatooth shark.
The role of prokaryotic microbial productivity in P cycling in the benthic boundary layer (BBL) of deep‐sea sediments (350–1,900 m bottom depths) was studied in the P‐impoverished southeastern ...Mediterranean Sea (SEMS) using sediment cores and incubation reactors. Our results show that orthophosphate (PO4) benthic fluxes were negative (consumption) at a rate of −11.0 ± 3.3 µmolem−2d−1, while the dissolved organic phosphate (DOP) flux was positive (production) at rate of 4.5 ± 1.6 µmolem−2d−1. Therefore, the SEMS sedimentary BBL acts as an active net sink for P, similar to other impoverished subtropical oceanic gyres, yet at much shallower water depths and much closer to the terrestrial margin. Considering the water column integrated P mass, and the sedimentary net removal fluxes of P, we calculated a turnover time of ∼90 years for the bottom water in the SEMS, which is similar to the deep water residence time in this basin. Apart abiotic removal of PO4 under oxic conditions (e.g., co‐precipitation with iron, forming iron‐phosphate minerals), prokaryotic microbial utilization played an important role in generating DOP through aerobic respiration in the BBL, resulting in a net release of DOP. Our study demonstrates that microbial communities in the BBL play an important role in regulating P concentrations, fluxes and forms in the energy‐starved environment of the SEMS seabed. These results may contribute to our understanding of water column P dynamics in the low nutrient low chlorophyll basins.
Plain Language Summary
The sediment‐water interface is a site of active nutrients exchange between the geosphere and the hydrosphere. We quantified fluxes of dissolved inorganic and organic phosphorous (PO4 and DOP) between the deep sediments and the overlying waters of the P‐limited southeastern Mediterranean Sea (SEMS) using sediment core incubations. Sediments were collected throughout the Israeli exclusive economic zone and analyzed for their pore‐water physicochemical characteristics. We also designed custom‐made incubation flux chambers and followed the PO4 and DOP dynamics as well as Prokaryotes heterotrophic production (HPP) for several days. We show that due to the low organic matter content and the well‐oxygenated conditions, the sediments of the SEMS function as a PO4 sink. This P sink is equal to a turnover time of ∼90 years, similar to the deep water residence time in this basin, hence contributing to the low concentration of PO4 in the SEMS bottom water. Aside from abiotic processes, such as, adsorption of PO4, HPP played a pivotal role in P‐recycling, resulting in a flux of dissolved organic P to the overlaying water. Organic molecules containing P and C are a known limiting factor for bacteria, and upon release from the sediment stimulated increased HPP.
Key Points
The sediments at the southeastern (SE) Mediterranean are net sink for dissolved P, where PO4 is rapidly consumed (sink) and dissolved organic phosphate (DOP) is gradually released
Bacterial production and P fluxes are positively coupled at the benthic boundary layer, highlighting their substantial role in P recycling
The trophic ecology of fourteen species of demersal fishes and six species of demersal decapod crustaceans from the continental slope and rise of the Southeastern Mediterranean Sea (SEMS) was ...examined using stable isotope analysis. Mean δ
13
C values among fish species varied by ca. 4.0‰, from -20.85‰ (
Macroramphosus scolopax
) to -16.57‰ and -16.89‰ (
Conger conger
and
Centrophorus granulosus
), showing an enrichment in
13
C as a function of depth (200 – 1400 m). Mean δ
13
C values of the crustaceans showed smaller variation, between -18.54‰ (
Aristeus antennatus
) and -16.38‰ (
Polycheles typhlops
). This suggests a shift from pelagic to regenerated benthic carbon sources with depth. Benthic carbon regeneration is further supported by the low benthic-pelagic POM-δ
13
C values, averaging -24.7 ± 1.2‰, and the mixing model results, presenting relatively low contribution of epipelagic POM to the deep-sea fauna. Mean δ
15
N values of fish and crustacean species ranged 7.91 ± 0.36‰ to 11.36 ± 0.39‰ and 5.96 ± 0.24‰ to 7.73 ± 0.46‰, respectively, resulting in trophic position estimates, occupying the third and the fourth trophic levels. Thus, despite the proximity to the more productive areas of the shelf, low number of trophic levels (TL~1.0) and narrow isotopic niche breadths (SEA
C
<1) were observed for demersal crustaceans (TL = 2.94 ± 0.18) and fishes (TL = 3.62 ± 0.31) in the study area – probably due to the ultra-oligotrophic state of the SEMS resulting in limited carbon sources. Our results, which provide the first trophic description of deep-sea megafauna in the SEMS, offer insight into the carbon sources and food web structure of deep-sea ecosystems in oligotrophic marginal seas, and can be further used in ecological modeling and support the sustainable management of marine resources in the deep Levantine Sea.
Here we explore the carbon and oxygen isotope compositions of the co-existing carbonate and phosphate fractions of fish tooth enameloid as a tool to reconstruct past aquatic fish environments and ...harvesting grounds. The enameloid oxygen isotope compositions of the phosphate fraction (δ18OPO4) vary by as much as ~4‰ for migratory marine fish such as gilthead seabream (Sparus aurata), predominantly reflecting the different saline habitats it occupies during its life cycle. The offset in enameloid Δ18OCO3-PO4 values of modern marine Sparidae and freshwater Cyprinidae from the Southeast Mediterranean region vary between 8.1 and 11.0‰, similar to values reported for modern sharks. The mean δ13C of modern adult S. aurata and Cyprinus carpio teeth of 0.1±0.4‰ and -6.1±0.7‰, respectively, mainly reflect the difference in δ13C of dissolved inorganic carbon (DIC) of the ambient water and dietary carbon sources. The enameloid Δ18OCO3-PO4 and δ13C values of ancient S. aurata (Holocene) and fossil Luciobarbus sp. (Cyprinidae; mid Pleistocene) teeth agree well with those of modern specimens, implying little diagenetic alteration of these tooth samples. Paired δ18OPO4-δ13C data from ancient S. aurata teeth indicate that hypersaline water bodies formed in the Levant region during the Late Holocene from typical Mediterranean coastal water with high evaporation rates and limited carbon input from terrestrial sources. Sparid tooth stable isotopes further suggest that coastal lagoons in the Eastern Mediterranean had already formed by the Early Holocene and were influenced by terrestrial carbon sources. Overall, combined enameloid oxygen and carbon isotope analysis of fish teeth is a powerful tool to infer the hydrologic evolution of aquatic environments and assess past fishing grounds of human populations in antiquity.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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