A New Desalination Pump Helps Define the pH of Ocean Worlds

Surface ocean marine dissolved organic matter (DOM) serves as an important reservoir of carbon (C), nitrogen (N), and phosphorus (P) in the global ocean, and is produced and consumed by both autotrophic and heterotrophic communities. While prior work has described distributions of dissolved organic carbon (DOC) and nitrogen (DON) concentrations, our understanding of DOC:DON:DOP stoichiometry in the global surface ocean has been limited by the availability of DOP concentration measurements. Here, we estimate mean surface ocean bulk and semi‐labile DOC:DON:DOP stoichiometry in biogeochemically and geographically defined regions using newly available marine DOM concentration databases. Global mean surface ocean bulk (C:N:P = 387:26:1) and semi‐labile (C:N:P = 179:20:1) DOM stoichiometries are higher than Redfield stoichiometry, with semi‐labile DOM stoichiometry similar to that of global mean surface ocean particulate organic matter (C:N:P = 160:21:1) reported in a recent compilation. DOM stoichiometry varies across ocean basins, ranging from 251:17:1 to 638:43:1 for bulk and 83:15:1 to 414:49:1 for semi‐labile DOM C:N:P, respectively. Surface ocean DOP concentration exhibits larger relative changes than DOC and DON, driving surface ocean gradients in DOC:DON:DOP stoichiometry. Inferred autotrophic consumption of DOP helps explain intra‐ and inter‐basin patterns of marine DOM C:N:P stoichiometry, with regional patterns of water column denitrification and iron supply influencing the biogeochemical conditions favoring DOP use as an organic nutrient. Specifically, surface ocean marine DOM exhibits increasingly P‐depleted stoichiometries from east to west in the Pacific and from south to north in the Atlantic, consistent with patterns of increasing P stress and alleviated iron stress.

To understand better the role of ocean surface chemical buffering capacity in mitigating the recent atmospheric CO2 rise, we investigated potentials of wintertime mixed-layer dissolved inorganic carbon (DIC) to increase after re-equilibration with decadal atmospheric CO2 rise and the corresponding anthropogenic CO2 accumulation rates, based upon carbonate system chemistry over the global ocean surface above the wintertime thermocline. This is an idealized study to quantify the isolated effect of atmospheric CO2 rise on the DIC content of the global mixed layer, assuming all else constant. Our results show that the potentials of wintertime DIC over the global open ocean surface to rise after re-equilibration with the elevated atmospheric CO2 mol fraction in a reference year 2000 ranged from 0.28 to 0.70 μmol kg−1 ppm−1 (ppm = parts of CO2 per million dry air), while the global mean wintertime sea surface DIC increase rate was close to 1.0 μmol kg−1 year−1. From 1995 to 2005, the decadal mean atmospheric CO2 rise implies an anthropogenic CO2 accumulation rate of 0.40 × 1015 g C year−1 within the global ocean surface. From the 1960s to 2000s, the air–sea re-equilibration-implied ocean surface anthropogenic CO2 accumulation rate may have increased by 46 % due to the accelerated atmospheric CO2 rise. However, the chemical buffering capacity within the ocean surface may have declined by 16 % during the same period.

Particulate organic carbon (POC) in the surface ocean contributes to understanding the global ocean carbon cycle system. The surface POC concentration can be effectively detected using satellites. In open oceans, the blue-to-green band ratio (BG) algorithm is often used to obtain global surface ocean POC concentrations. However, POC concentrations are underestimated in waters with complex optical environments. To generate a more accurate global POC mapping in the surface ocean, we developed a new ocean color algorithm using a mixed global-scale in situ POC dataset with the concentration ranging from 11.10 to 4389.28 mg/m3. The new algorithm (a-POC) was established to retrieve the POC concentration using the strong relationship between the absorption coefficient at 490 nm (a(490)) and POC, in which a(490) was from the Ocean Color Climate Change Initiative (OC-CCI) v5.0 suite. Afterward, the a-POC algorithm was applied to OC-CCI v5.0 data for special regions and the global ocean. The performances of the a-POC algorithm and the BG algorithm were compared by combining the match-ups of satellite data and in situ dataset. The results showed that the statistical parameters of the a-POC algorithm were similar to those of the BG algorithm in the Atlantic oligotrophic gyre regions, with a median absolute percentage deviation (MAPD) value of 22.04%. In the eastern coastal waters of the United States and the Chesapeake Bay, the POC concentration retrieved by the a-POC algorithm was highly consistent with the match-ups, and MAPD values were 33.06% and 26.11%. The a-POC algorithm was also applied to the Ocean and Land Color Instrument (OLCI) data pre-processed with different atmospheric correction algorithms to evaluate the universality. The result showed that the a-POC algorithm was robust and less sensitive to atmospheric correction than the BG algorithm.

Vertical eddy diffusion as a key mechanism for removing perfluorooctanoic acid (PFOA) from the global surface oceans

Positive feedbacks in climate processes can make it difficult to identify the primary drivers of climate phenomena. Some recent global climate model (GCM) studies address this issue by controlling the wind stress felt by the surface ocean such that the atmosphere and ocean become mechanically decoupled. Most mechanical decoupling studies have chosen to override wind stress with an annual climatology. In this study we introduce an alternative method of interannually varying overriding which maintains higher frequency momentum forcing of the surface ocean. Using a GCM (NCAR CESM1), we then assess the size of the biases associated with these two methods of overriding by comparing with a freely evolving control integration. We find that overriding with a climatology creates sea surface temperature (SST) biases throughout the global oceans on the order of ±1°C. This is substantially larger than the biases introduced by interannually varying overriding, especially in the tropical Pacific. We attribute the climatological overriding SST biases to a lack of synoptic and subseasonal variability, which causes the mixed layer to be too shallow throughout the global surface ocean. This shoaling of the mixed layer reduces the effective heat capacity of the surface ocean such that SST biases excite atmospheric feedbacks. These results have implications for the reinterpretation of past climatological wind stress overriding studies: past climate signals attributed to momentum coupling may in fact be spurious responses to SST biases.

The all-wave net radiation (Rn) on the ocean surface characterizes the available radiative energy balance and is important to understand the Earth’s climate system. Considering the shortcomings of available ocean surface Rn datasets (e.g., coarse spatial resolutions, discrepancy in accuracy, inconsistency, and short duration), a new long-term global daily Rn product at a spatial resolution of 0.05° from 1983 to 2020, as part of the Global High Resolution Ocean Surface Energy (GHOSE) products suite, was generated in this study by fusing several existing datasets including satellite and reanalysis products based on the comprehensive in situ measurements from 68 globally distributed moored buoy sites. Evaluation against in-situ measurements shows the root mean square difference, mean bias error and correlation coefficient squared of 23.56 Wm−2, 0.88 Wm−2 and 0.878. The global average ocean surface Rn over 1983–2020 is estimated to be 119.71 ± 2.78 Wm−2 with a significant increasing rate of 0.16 Wm−2 per year. GHOSE Rn product can be valuable for oceanic and climatic studies.

We present results that improve the estimates of the global net sea‐to‐air flux, global oceanic emission, global oceanic uptake, and partial atmospheric lifetime of methyl chloride (CH3Cl) with respect to oceanic loss. This study includes improved parameterizations for solubility and saturation anomaly‐sea surface temperature relationships for CH3Cl, along with the use of an updated gas transfer velocity from a recent study. By measuring solubilities of CH3Cl in pure water and seawater over a temperature range from 0°C to 40°C, we obtained a new solubility function with both temperature and salinity dependencies. We also developed a new parameterization of seasonal CH3Cl saturation anomaly (∆%) as a function of both sea surface temperature and wind speed using data from 10 different cruises with an extensive coverage in the global surface ocean. Using the new solubility function and the new seasonal ∆%‐(SST, wind speed) relationships, we estimated the global net sea‐to‐air flux of CH3Cl at 335 (210 to 480) Gg yr−1. For the first time, the global flux of CH3Cl was broken into a unidirectional gross emission and a unidirectional gross uptake, which were estimated at 700 (510 to 910) Gg yr−1 and −370 (−430 to −300) Gg yr−1. The partial atmospheric lifetime of CH3Cl with respect to the oceanic uptake was revised to 12 (10–15) years, resulting in a revision on the atmospheric lifetime of CH3Cl from the previous estimate of 1.0 year to 1.2 years.

Abiotic fixation of atmospheric dinitrogen to ammonia is important in prebiotic chemistry and biological evolution in the Hadean and Archean oceans. Though it is widely accepted that nitrate (NO3−) was generated in the early atmospheres, the stable pathways of ammonia production from nitrate deposited in the early oceans remain unknown. This paper reports results of the first experiments simulating high-temperature, high-pressure reactions between nitrate and komatiite to find probable chemical pathways to deliver ammonia to the vent–ocean interface of komatiite-hosted hydrothermal systems and the global ocean on geological timescales. The fluid chemistry and mineralogy of the komatiite–H2O–NO3− system show iron-mediated production of ammonia from nitrate with yields of 10% at 250 °C and 350 °C, 500 bars. The komatiite–H2O–NO3– system also generated H2-rich and alkaline fluids, well-known prerequisites for prebiotic and primordial metabolisms, at lower temperatures than the komatiite–H2O–CO2 system. We estimate the ammonia flux from the komatiite-hosted systems to be 105–1010 mol/y in the early oceans. If the nitrate concentration in the early oceans was greater than 10 μmol/kg, the long-term production of ammonia through thermochemical nitrate reduction for the first billion years might have allowed the subsequent development of an early biosphere in the global surface ocean. Our results imply that komatiite-hosted systems might have impacted not only H2-based chemosynthetic ecosystems at the vent-ocean interface but also photosynthetic ecosystems on the early Earth.

Abstract. Here, the Copernicus Ocean State Report offers detailed scientific analysis of the ocean under climate change, ocean variability, and ocean extremes. This evidence-based reporting is based on a set of key ocean indicators such as sea surface temperature, sea level rise, ocean heat content, ocean acidification, and sea ice extent. Moreover, key indicators for ocean variability such as the El Niño–Southern Oscillation and major ocean current systems such as the Atlantic Meridional Overturning Circulation are tackled. Major results show that the global ocean's sea surface temperature continues to steadily increase, particularly in the Northern Hemisphere, with a global warming rate of 0.13 ± 0.01 °C per decade from 1982 to 2023. Since around the 1970s, the ocean warming trend has intensified, doubling its rate over the past 2 decades. Concurrently, global mean sea level has risen significantly at intensifying rates from 2.1 mm yr−1 in the 1990s to 4.3 mm yr−1 in recent years, with regional disparities. The Arctic Ocean has faced unprecedented sea ice loss and warming, while Antarctic sea ice has reached record lows. Ocean acidification has progressed, decreasing pH at a rate of −0.017 per decade. Marine heatwaves have become more frequent, intense, and extensive, affecting up to 80 % of the global ocean surface annually. Despite significant variability, extreme ocean surface wind speeds have been prevalent, particularly in the North Atlantic, North Pacific, and Southern Ocean. The Atlantic Meridional Overturning Circulation shows no significant decline but varies substantially. In 2023, La Niña conditions have transitioned to El Niño conditions in the Pacific Ocean.

Risks of floating microplastic in the global ocean

The chemistry of the global ocean is rapidly changing due to the uptake of anthropogenic carbon dioxide (CO2). This process, commonly referred to as ocean acidification (OA), is negatively impacting many marine species and ecosystems. In this study, we combine observations in the global surface ocean collected by NOAA Pacific Marine Environmental Laboratory and Atlantic Oceanographic and Meteorological Laboratory scientists and their national and international colleagues over the past four decades, along with model outputs, to provide a high-resolution, regionally varying view of global surface ocean carbon dioxide fugacity, carbonate ion content, total hydrogen ion content, pH on total scale, and aragonite and calcite saturation states on selected time intervals from 1961 to 2020. We discuss the major roles played by air-sea anthropogenic CO2 uptake, warming, local upwelling processes, and declining buffer capacity in controlling the spatial and temporal variability of these parameters. These changes are occurring rapidly in regions that would normally be considered OA refugia, thus threatening the protection that these regions provide for stocks of sensitive species and increasing the potential for expanding biological impacts.

Global ocean wind power has recently been assessed (W. T. Liu et al., 2008) using scatterometry‐based 10 m winds. We characterize, for the first time, wind power at 80 m (typical wind turbine hub height) above the global ocean surface, and account for the effects of surface layer stability. Accounting for realistic turbine height and atmospheric stability increases mean global ocean wind power by +58% and −4%, respectively. Our best estimate of mean global ocean wind power is 731 W m−2, about 50% greater than the 487 W m−2 based on previous methods. 80 m wind power is 1.2–1.5 times 10 m power equatorward of 30° latitude, between 1.4 and 1.7 times 10 m power in wintertime storm track regions and >6 times 10 m power in stable regimes east of continents. These results are relatively insensitive to methodology as wind power calculated using a fitted Weibull probability density function is within 10% of power calculated from discrete wind speed measurements over most of the global oceans.

Hydrothermal evolution and ore genesis of the Hongshi copper deposit in the East Tianshan Orogenic Belt, Xinjiang, NW China: Constraints from ore geology, fluid inclusion geochemistry and H–O–S–He–Ar isotopes

Genesis of the Hardat Tolgoi Ag-Pb-Zn deposit, Inner Mongolia, northeast China: Constraints from geology, fluid inclusions, and C-O-S-Pb isotope systematics

As two most important metrics for ocean acidification (OA), both pH and calcium carbonate mineral saturation states (Ω) respond sensitively to anthropogenic carbon dioxide (CO2). However, contrary to intuition, they are often out of phase in the global surface ocean, both spatially and seasonally. For example, during warm seasons, Ω is lowest at high‐latitude seas where there are very high pH values, challenging our understanding that high‐latitude seas are a bellwether for global OA. To explain this phenomenon, we separate spatial and seasonal variations of both pH and Ω into thermal components mainly associated with internal acid‐base equilibrium of seawater CO2 systems, and nonthermal components mainly associated with external CO2 addition/removal using a global surface ocean climatological data set. We find that surface pH change is controlled by the balance between its thermal and nonthermal components, which are out of phase but comparable in magnitude. In contrast, surface Ω change is dominated by its nonthermal components, with its thermal components in phase and significantly smaller in magnitude. These findings explain why surface ocean pH and Ω are often out of phase in spatial patterns and seasonal cycles. When pH is primarily controlled by nonthermal components e.g., gas exchange, mixing and biology, pH and Ω will be in phase because their nonthermal components are intrinsically in phase. In comparison, when pH is primarily controlled by thermal components for example, rapid seasonal cooling or warming, pH and Ω will be out of phase because thermal and nonthermal components of pH are out‐of‐phase in nature.