Deep Open Ocean Research Articles

Synergistic innovations enabled the radiation of anglerfishes in the deep open ocean

Major ecological transitions are thought to fuel diversification, but whether they are contingent on the evolution of certain traits called key innovations1 is unclear. Key innovations are routinely invoked to explain how lineages rapidly exploit new ecological opportunities.1,2,3 However, investigations of key innovations often focus on single traits rather than considering trait combinations that collectively produce effects of interest.4 Here, we investigate the evolution of synergistic trait interactions in anglerfishes, which include one of the most species-rich vertebrate clades in the bathypelagic, or "midnight," zone of the deep sea: Ceratioidea.5 Ceratioids are the only vertebrates that possess sexual parasitism, wherein males temporarily attach or permanently fuse to females to mate.6,7 We show that the rapid transition of ancestrally benthic anglerfishes into pelagic habitats occurred during a period of major global warming 50-35 million years ago.8,9 This transition coincided with the origins of sexual parasitism, which is thought to increase the probability of successful reproduction once a mate is found in the midnight zone, Earth's largest habitat.5,6,7 Our reconstruction of the evolutionary history of anglerfishes and the loss of immune genes support that permanently fusing clades have convergently degenerated their adaptive immunity. We find that degenerate adaptive immune genes and sexual body size dimorphism, both variably present in anglerfishes outside the ceratioid radiation, likely promoted their transition into the bathypelagic zone. These results show how traits from separate physiological, morphological, and reproductive systems can interact synergistically to drive major transitions and subsequent diversification in novel environments.

Seawater Pb concentration and isotopic composition response to daily time scale dust storms in the Gulf of Aqaba, Red Sea

Lead (Pb) is a primary tracer of natural and anthropogenic processes in the marine environment, with atmospheric deposition being one of its main sources to open ocean surface waters. However, the impact of short-term (daily) dust storms on the oceanic water column is poorly constrained due to the typically low sampling temporal resolution in deep open ocean settings. The Gulf of Aqaba (GoA), northern Red Sea, is a deep oligotrophic water body surrounded by hyper-arid deserts with no major tributaries, and hence its surface waters receive limited terrigenous input, except from settling atmospheric dust particles. The GoA is highly accessible and therefore provides the opportunity to study the dynamics of seawater Pb chemistry across abrupt and short periods of enhanced atmospheric deposition.Here, we report a highly resolved time series of vertical profiles of dissolved Pb concentrations and isotopic compositions across daily-timescale dust storm events that occurred during 2018. GoA Pb concentrations range between 19 and 85 pmol kg−1, and the isotopic compositions of 206Pb/207Pb and 208Pb/206Pb are in the range of 1.163–1.190 and 2.062–2.093, respectively. These compositions reflect a mixture of multiple end members: seafloor sediments and open Red Sea waters, which modulate the long-term deep-water composition of GoA Pb, and settling aerosols, which shift the seawater composition towards anthropogenic values. The results show that dust storms impose strong perturbations of seawater compositions towards the anthropogenic aerosols end member, inducing increases of up to 54% in the Pb inventory in the upper water column. We propose a short-term dissolution-scavenging mechanism, whereby upon dust-seawater impact, the majority of the aerosol's soluble anthropogenic phases rapidly dissolve. The peak in the aerosol derived isotopic shift in the mixed layer is reached after 3–4 days. Simultaneously, Pb is re-adsorbed onto the sinking dust mineral particulates. Post dust storm Pb leaching and scavenging rates are modeled, yielding quantitative constraints on the connection between increasing dust loads and seawater Pb concentrations and isotopic compositions. Our findings demonstrate the short-term variable Pb response to dust storms and should be applied when interpreting open ocean surface water Pb patterns.

Reef-associated fishes have more maneuverable body shapes at a macroevolutionary scale

Marine habitats vary widely in structure, from incredibly complex coral reefs to simpler deep water and open ocean habitats. Hydromechanical models of swimming kinematics and microevolutionary studies suggest that these habitats select for different body shape characteristics. Fishes living in simple habitats are predicted to experience selection for energy-efficient sustained swimming, which can be achieved by fusiform body shapes. In contrast, fishes living in complex habitats are predicted to be under selection for maneuverability, which can be enhanced by deep-bodied and laterally compressed forms. To look for a signature of these processes at a broad macroevolutionary scale, we quantified the body shapes of 3322 species of marine teleostean fishes using a series of linear measurements. We scored each species for whether they were reef-associated or not and tested for morphological differences using a phylogenetic framework. Our results confirmed significant overall shape differences between reef-associated teleosts and those occupying structurally simpler marine habitats. Reef-associated species have, on average, deeper bodies and higher depth-to-width ratios, while non-reef species are more streamlined with narrower and shallower caudal peduncles. Despite the numerous evolutionary forces that may influence body shapes on a broad macroevolutionary scale, our results reveal differences in body shapes between reef-associated and non-reef species that are consistent with hydromechanical models of swimming kinematics as well as with microevolutionary patterns.

Abundance and characteristics of microfibers detected in sediment trap material from the deep subtropical North Atlantic Ocean

Plastics and microplastics increasingly gain importance due to their perils and wide distribution in the marine environment. Microfibers account for the largest percentage of anthropogenic-induced microparticles, which inter alia, consist of plastic, and are found in deep-sea sediments. However, the sinking of fibers from the surface through the water column to the seafloor is still poorly understood. The present study investigates microfibers extracted from sediment trap samples, which were deployed in the North Atlantic Subtropical Gyre (NASG). The average result of eleven analyzed samples showed 913 microfibers per gram of collected particle flux material, with a predominant fiber length shorter than 1 mm (75.6%) and a distribution maximum between 0.2 and 0.4 mm. Further, the average number of microfibers found in this study was used to derive microfiber fluxes for the NASG based on the deployment time of the sediment trap. Extrapolating the computed flux of 94 microfibers m−2 day−1 to the entire NASG area would correspond to a total microfiber mass flux of 9800 t a−1 or 73 × 1013 microfibers a−1 of sinking microfibers through the water column. These findings offer an extended application of sediment traps to monitor microfiber fluxes, which reveals the opportunity to investigate the mechanism driving sinking of microfibers and microplastics into the deep open ocean.

The Role of Tides in Ocean‐Ice Shelf Interactions in the Southwestern Weddell Sea

AbstractTo investigate the role of tides in Weddell Sea ocean‐ice shelf melt interactions, and resulting consequences for ocean properties and sea ice interactions, we develop a regional ocean‐sea ice model configuration, with time‐varying ocean boundary and atmospheric forcing, including the deep open ocean (at 2.5–4 km horizontal resolution), the southwestern continental shelf (≈2.5 km), and the adjacent cavities of eastern Weddell, Larsen, and Filchner‐Ronne ice shelves (FRIS, 1.5–2.5 km). Simulated circulation, water mass, and ice shelf melt properties compare overall well with available open ocean and cavity observational knowledge. Tides are shown to enhance the kinetic energy of the time‐varying flow in contact with the ice shelves, thereby increasing melt. This dynamically driven impact of tides on net melting is to almost 90% compensated by cooling through the meltwater that is produced but not quickly exported from regions of melting in the Weddell Sea cold‐cavity regime. The resulting systematic tide‐driven enhancement of both produced meltwater and its refreezing on ascending branches of, especially the FRIS, cavity circulation acts to increase net ice shelf melting (by 50% in respect to the state without tides, ≈50 Gt yr−1). In addition, tides also increase the melt‐induced FRIS cavity circulation, and the meltwater export by the FRIS outflow. Simulations suggest attendant changes on the open‐ocean southwestern continental shelf, characterized by overall freshening and small year‐round sea ice thickening, as well as in the deep southwestern Weddell Sea in the form of a marked freshening of newly formed bottom waters.

BPOP-v1 model: exploring the impact of changes in the biological pump on the shelf sea and ocean nutrient and redox state

Abstract. The biological pump of the ocean has changed over Earth's history, from one dominated by prokaryotes to one involving a mixture of prokaryotes and eukaryotes with trophic structure. Changes in the biological pump are in turn hypothesized to have caused important changes in the nutrient and redox properties of the ocean. To explore these hypotheses, we present here a new box model including oxygen (O), phosphorus (P) and a dynamical biological pump. Our Biological Pump, Oxygen and Phosphorus (BPOP) model accounts for two – small and large – organic matter species generated by production and coagulation, respectively. Export and burial of these particles are regulated by a remineralization length (zrem) scheme. We independently vary zrem of small and large particles in order to study how changes in sinking speeds and remineralization rates affect the major biogeochemical fluxes and O and P ocean concentrations. Modeled O and P budgets and fluxes lie reasonably close to present estimates for zrem in the range of currently measured values. Our results highlight that relatively small changes in zrem of the large particles can have important impacts on the O and P ocean availability and support the idea that an early ocean dominated by small particles was nutrient rich due to the inefficient removal of P to sediments. The results also suggest that extremely low oxygen concentrations in the shelf can coexist with an oxygenated deep open ocean for realistic values of zrem, especially for large values of the small-particle zrem. This could challenge conventional interpretations that the Proterozoic deep ocean was anoxic, which are derived from shelf and slope sediment redox data. This simple and computationally inexpensive model is a promising tool to investigate the impact of changes in the organic matter sinking and remineralization rates as well as changes in physical processes coupled with the biological pump in a variety of case studies.

Behaviour of chromium and chromium isotopes during estuarine mixing in the Beaulieu Estuary, UK

Rivers are the principal source of chromium (Cr) to seawater and the Cr isotopic signatures of ancient marine sediments are widely considered to provide a record of the presence or absence of oxidative weathering processes on land. This assumes, however, that the δ53Cr value of river water is faithfully transferred to the oceans and is not modified in the estuarine mixing zone. To test this assumption we have determined the concentration and δ53Cr values of inorganic Cr (Cr(III) + Cr(VI)), and also Cr speciation for water samples collected within the estuarine mixing zone of the Beaulieu River, UK. The δ53Cr values of dissolved inorganic Cr ranged from −0.59 to 1.68‰, Cr(VI) concentrations from 0.39 to 1.83 nmolkg−1 and Cr(III) concentrations from 0.11 to 3.21 nmolkg−1. Both Cr(VI) concentrations and δ53Cr values increased linearly as a function of salinity, while Cr(III) concentrations decreased linearly with salinity. Thus δ53Cr, Cr(III) and Cr(VI) all showed conservative behaviour in the estuarine mixing zone, and the δ53Cr signature of Beaulieu River water was modified only by mixing between the river and seawater endmembers. The calculated average δ53Cr value of the river water endmember (−0.39 ± 0.08‰) was, however, lower than the range that has been observed in other rivers, which we attribute to input of organically-bound Cr(III) released by anoxic weathering processes. This is supported by the fact that Cr recovered by UV irradiation was found to have low δ53Cr values (−0.11 to −0.75‰). While input of Cr from anoxic weathering processes is unlikely to be an important source of Cr to the oceans today, this suggests that processes other than oxidative weathering may have an influence on the δ53Cr values of estuarine and coastal waters on the local scale. The δ53Cr value of the coastal seawater endmember (1.6 ± 0.4‰) was also higher than the range observed in the deep open ocean, due to in situ biogeochemical cycling of Cr. These factors need to be considered in the interpretation of marine sedimentary δ53Cr records.

Around Buzzards Bay to a World of Ocean Science: A Personal Perspective

AbstractReading books, a chemistry set, living by the sea, and a chance attendance by John Farrington at a seminar led to doctor of philosophy studies in ocean sciences at the Graduate School of Oceanography, University of Rhode Island, with a focus on organic chemicals in estuarine ecosystems. An unexpected discovery of a chronic oil pollution problem during these studies set a course for a career of research at the Woods Hole Oceanographic Institution focused on the biogeochemistry of biogenic organic chemicals and organic chemicals of environmental concern such as oil chemicals and polychlorinated biphenyls. This involved cruises to deep open ocean, continental margin, and coastal ecosystems. Several times, the research was influenced by unexpected observations opening important avenues of inquiry. Details of portions of the ocean carbon cycle, especially water column particles and surface sediments, were unraveled. Environmental quality‐related research led to activities at the science‐policy interface. These laboratory group efforts have been recognized by my election as a fellow of the American Geophysical Union and the American Association for the Advancement of Science, among other recognitions.

Meridional distribution of dissolved manganese in the tropical and equatorial Pacific

Abstract The distribution of dissolved Mn (dMn) was studied in the Tropical and Equatorial Pacific along a meridional transect beginning at station ALOHA (22.45°N, 158°W) extending southwards to 7°S along 158°W. Results show that in the surface ocean ( 6000 km) from the continents, which suggests that dMn in the deep open ocean is strongly affected by remineralization. The dMn:AOU linear relationship (n = 37, R = 0.87) that we found in this work is consistent with culture studies and can be applied to Mn models to reproduce the observed open-ocean Mn concentrations in deep waters.

NUMERICAL FLOW MODELING AROUND OKINAWA FROM CORAL REEF AREA TO OPEN OCEAN

Coastal area along the Okinawa sea is formed from coral reefs. In the area, coastal flows are generated by various factors of tide, wave, wind, river discharge and so on. In the offshore areas, oceanic currents including the Kuroshio also influence the coastal flows, because of the openness. Thus, the flow pattern becomes complicated by such external forces. To simulate the flow pattern of the Okinawa sea by numerical flow modeling, the model needs to deal with the various external forces from shallow coral reef area to deep open ocean. Additionally, steep slope exists in the offshore end of coral reef. In such region, we have to be careful because flow simulation is likely unstable. This study intends to develop the numerical flow model which is applicable to the Okinawa sea, and its performance has been tested in the several sea areas. In addition, field observations were carried out to investigate the flow phenomena and to verify the model accuracy. The result of filed observation and its comparing with the simulation is shown.

Aeolian transport and deposition of plant wax n-alkanes across the tropical North Atlantic Ocean

Long chain n-alkanes are terrestrial higher plant biomarkers analysed in marine sedimentary archives to reconstruct continental palaeoclimatic and palaeohydrological conditions. Latitudinal variation in their concentration and distribution in marine sediments relatively close to the continent has been widely studied, but little is known on the extent to which this continental signal extends to the ocean. Furthermore, no studies have examined the seasonal variation in the deposition of these biomarkers in marine sediments. Here we studied longitudinal variation in the composition of long chain n-alkanes and two other terrestrial higher plant biomarkers (long chain n-alkanols and long chain fatty acids) in atmospheric particles, as well as longitudinal and seasonal variation in long chain n-alkanes in sinking particles in the ocean at different water depths and in surface sediments, all collected along a 12°N transect across the tropical North Atlantic Ocean. The highest abundance of all three biomarker classes was closest to the African coast, as expected, because they are transported with Saharan dust and the largest part of the dust is deposited close to the source. At this proximal location, the seasonal variability in long chain n-alkane flux and the chain length distribution of the n-alkanes in sinking particles was most pronounced, due to seasonal change in the dust source or to change in vegetation composition in the source area, related to the position of the Intertropical Convergence Zone (ITCZ). In contrast, in the open ocean the seasonal variability in both the long chain n-alkane flux and chain length distribution of the n-alkanes was low. The abundance of the alkanes was also lower, as expected because of the larger source-to-sink distance. At the western part of the transect, close to South America, we found an additional source of the alkanes in the sinking particles during spring and autumn in the year 2013. The δ13C values of the alkanes in the surface sediment closest to the South American continent indicated that the isotope signal was likely derived from C3 vegetation from the Amazon, implying an input from the Amazon River, as there is no significant aeolian input from South America there since the prevailing wind direction is from the east. Finally, the concentration of the alkanes was similar in the material collected from the atmosphere, the particles collected while settling through the marine water column, and in the surface sediments, providing evidence that degradation of long chain n-alkanes from the atmosphere to settling at the sediment–water interface at deep open ocean sites is minimal.

Homeward bound: fish larvae use dispersal corridors when settling on coral reefs

Homeward bound: fish larvae use dispersal corridors when settling on coral reefs

Autonomous Underwater Vehicle Motion Response: A Nonacoustic Tool for Blue Water Navigation

AbstractAutonomous underwater vehicles (AUVs) use secondary velocity over ground measurements to aid the Inertial Navigation System (INS) to avoid unbounded drift in the point-to-point navigation solution. When operating in deep open ocean (i.e., in blue water—beyond the frequency-specific instrument range), the velocity measurements are either based on water column velocities or completely unavailable. In such scenarios, the velocity-relative-to-water measurements from an acoustic Doppler current profiler (ADCP) are often used for INS aiding. ADCPs have a blanking distance (typically ranging between 0.5 and 5 m) in proximity to the device in which the flow velocity data are undetectable. Hence, water velocities used to aid the INS solution can be significantly different from that near the vehicle and are subjected to significant noise. Previously, the authors introduced a nonacoustic method to calculate the water velocity components of a turbulent water column within the ADCP dead zone using the AUV motion response (referred to as the WVAM method). The current study analyzes the feasibility of incorporating the WVAM method within the INS by investigating the accuracy of it at different turbulence levels of the water column. Findings of this work demonstrate that the threshold limits of the method can be improved in the nonlinear ranges (i.e., at low and high levels of energy); however, by estimating a more accurate representation of vehicle hydrodynamic coefficients, this method has proven robust in a range of tidally induced flow conditions. The WVAM method, in its current state, offers significant potential to make a key contribution to blue water navigation when integrated within the vehicle's INS.

RETROSPECTS AND PROSPECTS OF MARINE GEOLOGY IN CHINA OVER AND BEYOND THIRTY YEARS

Launched in 1981,the journal Marine and Quaternary Geology published thirty volumes,and like tree rings the thirty volumes have recorded the development of marine geology over the 30 years of China's reform and opening-up.Today the Chinese marine science community is on the march to the deep open ocean,getting active on the ocean science frontiers.As shown by recent discoveries,the deep sea floor provides a passageway between the surface and interior parts of the Earth system,and its understanding has become a bottleneck in the Earth system studies.On the other hand,the marine science is now at the transition from expedition to observation,and the sea-floor observatories are building up the third platform for the Earth system observation.Looking forward to the 30 years ahead,the Marine and Quaternary Geology will mirror the progress of marine geology in China,keeping track of its growth in the international scientific arena.

Global Patterns of Bacterial Beta-Diversity in Seafloor and Seawater Ecosystems

BackgroundMarine microbial communities have been essential contributors to global biomass, nutrient cycling, and biodiversity since the early history of Earth, but so far their community distribution patterns remain unknown in most marine ecosystems.Methodology/Principal FindingsThe synthesis of 9.6 million bacterial V6-rRNA amplicons for 509 samples that span the global ocean's surface to the deep-sea floor shows that pelagic and benthic communities greatly differ, at all taxonomic levels, and share <10% bacterial types defined at 3% sequence similarity level. Surface and deep water, coastal and open ocean, and anoxic and oxic ecosystems host distinct communities that reflect productivity, land influences and other environmental constraints such as oxygen availability. The high variability of bacterial community composition specific to vent and coastal ecosystems reflects the heterogeneity and dynamic nature of these habitats. Both pelagic and benthic bacterial community distributions correlate with surface water productivity, reflecting the coupling between both realms by particle export. Also, differences in physical mixing may play a fundamental role in the distribution patterns of marine bacteria, as benthic communities showed a higher dissimilarity with increasing distance than pelagic communities.Conclusions/SignificanceThis first synthesis of global bacterial distribution across different ecosystems of the World's oceans shows remarkable horizontal and vertical large-scale patterns in bacterial communities. This opens interesting perspectives for the definition of biogeographical biomes for bacteria of ocean waters and the seabed.

A multiple instrument approach to quantifying the movement patterns and habitat use of tiger (Galeocerdo cuvier) and Galapagos sharks (Carcharhinus galapagensis) at French Frigate Shoals, Hawaii

We equipped individual tiger (Galeocerdo cuvier Peron and Lesueur, 1822) and Galapagos (Carcharhinus galapagensis Snodgrass and Heller, 1905) sharks with both acoustic and satellite transmitters to quantify their long-term movements in the Papahanaumokuakea Marine National Monument (Northwestern Hawaiian Islands). Tiger sharks exhibited two broad patterns of behavior. Some individuals were detected at French Frigate Shoals (FFS) year round, whereas others visited FFS atoll in summer to forage on fledging albatross, then swam thousands of kilometers along the Hawaiian chain, or out into open ocean to the North Pacific transition zone chlorophyll front, before returning to FFS in subsequent years. These patterns suggest tiger sharks may use cognitive maps to navigate between distant foraging areas. Different patterns of spatial behavior may arise because cognitive maps are built up through individual exploration, and each tiger shark learns a unique combination of foraging sites. Galapagos shark detections were all associated with FFS, suggesting these sharks may be more resident around oceanic islands. Both Galapagos and tiger sharks primarily used the mixed layer (<100 m depth) and made occasional deeper dives through the thermocline down to 680 m. Results show reef-associated sharks utilize a wide variety of habitats ranging from shallow atoll lagoons to deep reefs and open ocean and may provide important trophic links between these habitats.

Excess total organic carbon in the intermediate water of the South China Sea and its export to the North Pacific

Depth profiles of total organic carbon (TOC) were measured in spring (2005) and winter (2006) in the South China Sea (SCS), the largest marginal sea adjacent to the North Western Pacific (NWP). Compared to TOC profiles in the NWP, excess TOC (3.2 ± 1.1 μmol kg−1) was revealed in the intermediate layer of the SCS at σθ ∼ 27.2–27.6 (∼1000–1500 m). Below the depth of 2000 m, TOC concentrations were identical between the SCS and the NWP. Based on a one‐dimensional steady state diffusion advection model constrained by potential temperature, we estimated a net TOC production rate of 0.12 ± 0.04 μmol kg−1 yr−1 to maintain this excess. A positive relationship between TOC and apparent oxygen utilization in the SCS deep water lent support to such a model‐derived TOC production. This excess TOC in the out‐flowing intermediate water may carry 3.1 ± 2.1 Tg C yr−1 of organic carbon out from the SCS and potentially into the deep open ocean. In light of the short residence time of the SCS deep water, the exported TOC was likely from the recently fixed organic carbon within the SCS. The export of such organic carbon, thereby less likely to return to the atmosphere may therefore contribute significantly to the carbon sequestration in the SCS.

Metrics of hurricane-ocean interaction: vertically-integrated or vertically-averaged ocean temperature?

Abstract. The ocean thermal field is often represented in hurricane-ocean interaction by a metric termed upper Ocean Heat Content (OHC), the vertical integral of ocean temperature in excess of 26°C. High values of OHC have proven useful for identifying ocean regions that are especially favorable for hurricane intensification. Nevertheless, it is argued here that a more direct and robust metric of the ocean thermal field may be afforded by a vertical average of temperature. In the simplest version, dubbed T100, the averaging is from the surface to 100 m, a typical depth of vertical mixing by a category 3 hurricane. OHC and T100 are well correlated over the deep open ocean in the high range of OHC, ≥75 kJ cm−2. They are poorly correlated in the low range of OHC, ≤50 kJ cm−2, in part because OHC is degenerate when evaluated on cool ocean regions, ≤26°C. OHC and T100 can be qualitatively different also over shallow continental shelves: OHC will generally indicate comparatively low values regardless of the ocean temperature, while T100 will take on high values over a shelf that is warm and upwelling neutral or negative. In so far as the ocean thermal field alone is concerned, these warm, shallow continental shelves would appear to be as favorable for hurricane intensification as are warm, deep ocean regions.

Winkler's method overestimates dissolved oxygen in seawater: Iodate interference and its oceanographic implications

Dissolved oxygen in seawater has been determined by using the Winkler's reaction scheme for decades. An interference in this reaction scheme that has been heretofore overlooked is the presence of naturally occurring iodate in seawater. Each mole of iodate can result in an apparent presence of 1.5 mol of dissolved oxygen. At the concentrations of iodate in the surface and deep open ocean, it can lead to an overestimation of 0.52 ± 0.15 and 0.63 ± 0.05 μmol kg − 1 of oxygen in these waters respectively. In coastal and inshore waters, the effect is less predictable as the concentration of iodate is more variable. The solubility of oxygen in seawater was likely overestimated in data sources that were based on the Winkler's reaction scheme for the determination of oxygen. The solubility equation of García and Gordon [Garcia H.E., Gordon, L.I., 1992. Oxygen solubility in seawater: Better fitting equations. Limnol. Oceanogr. 37, 1307–1312] derived from the results of Benson and Krause [Benson, F.B., Krause, D. Jr., 1984. The concentration and isotopic fractionation of oxygen dissolved in freshwater and seawater in equilibrium with the atmosphere. Limnol. Oceanogr. 29, 620–632] is free from this source of error and is recommended for general use. By neglecting the presence of iodate, the average global super-saturation of oxygen in the surface oceans and the corresponding efflux of oxygen to the atmosphere both have been overestimated by about 8%. Regionally, in areas where the degree of super-saturation or under-saturation of oxygen in the surface water is small, such as in the tropical oceans, the net air–sea exchange flux can be grossly under- or overestimated. Even the estimated direction of the exchange can be reversed. Furthermore, the presence of iodate can lead to an overestimation of the saturation anomaly of oxygen in the upper ocean attributed to biological production by 0.23 ± 0.07%. AOU may have been underestimated by 0.52 ± 0.15 and 0.63 ± 0.05 μmol kg − 1 in the surface mixed layer and deep water, while preformed phosphate and preformed nitrate may have been overestimated by 0.004 ± 0.001 and 0.06 ± 0.02 μmol kg − 1 in the surface mixed layer, and 0.005 ± 0.0004 and 0.073 ± 0.006 μmol kg − 1 in the deep water. These are small but not negligible corrections, especially in areas where the values of these parameters are small. At the increasing level of sophistication in the interpretation of oxygen data, this source of error should now be taken into account. Nevertheless, in order to avoid confusion, an internationally accepted standard needs to be adopted before these corrections can be applied.

Reprint of Dissolved organic carbon and nitrogen in the Western Black Sea

Dissolved organic carbon and nitrogen (DOC and DON) concentrations were measured in the Black Sea during May–June 2001. Sampling was conducted along a Shelf–Gyre transect, and was focused at the suboxic–anoxic interface at the deep stations; hypotheses were tested regarding trends in these variables across the transect and between sub-surface water layers. DOC and DON concentrations were higher (272 μM and 15 μM, respectively) on the Shelf compared to the Gyre (200 μM and 11 μM, respectively), as a result of terrigenous inputs and in situ net production. The bulk DOC:DON ratio was constant with distance and depth (approximately 15–19). DOM concentrations decreased with depth (average anoxic layer concentrations of 123 μM and 6.1 μM for DOC and DON, respectively), in contrast to earlier observations of increasing DOC concentration with depth. The deep Basin (2000 m) DOC concentrations were high compared to deep open ocean values (120 vs 45 μM). We suggest that the high deep DOC is a product of mixing of terrigenous (300 μM) and Aegean Sea (60 μM) DOC, with some in situ decomposition over the 600 year residence time for the deep water mass. High surface concentrations of DOC and DON and high DOC:DON ratios throughout the sampling region indicate the pervasive influence of remnant terrigenous DOM with some net production. The timescales for DOM Shelf–Basin exchange and decomposition could not be estimated due to a lack of geochemical tracer data.