The western Arctic Ocean is known to be nitrate deficient relative to phosphate but the decadal trend and the processes contributing to the deficit are not clear. To investigate changes in this ...extreme nitrate deficit of over 10 μmol/kg and its causal mechanisms, nutrient concentrations were examined along a transect spanning the Bering Basin, the Bering–Chukchi Shelf, and the western Arctic Ocean Basin over the last two decades (1994–2018). The results show that the extreme nitrate deficit has extended to greater depths and further north during the past two decades, which coincided with the expansion of Pacific water in the western Arctic Ocean. Subsurface nutrient stocks in the basin areas appear to have increased, but are accompanied by a larger nitrate deficit, which may be due to stronger shelf denitrification. This nitrate loss (∆N) caused by shelf denitrification was estimated to be 7.3 ± 0.1 μmol/kg during the interval 2012–2018, which was ∼10% higher than that in 1994. This suggests an intensification of denitrification on this marginal shelf under climatic and environmental change in the Arctic Ocean.
Plain Language Summary
Prominent nitrate deficits relative to phosphate of over 10 μmol/kg in the Arctic Ocean are caused by a combination of nitrate loss by denitrification and a pre‐existing nitrate deficit in the inflowing Pacific waters. Over the last two decades (1994–2018), this extreme nitrate deficit extended to greater depths and further north, which coincided with the expansion of Pacific water into the western Arctic Ocean. Meanwhile, subsurface nutrient stocks have increased, however followed by a larger nitrate deficit, which may be due to stronger shelf denitrification in the western Arctic Ocean.
Key Points
Prominent nitrate deficits of over 10 μmol/kg expanded to greater depths and further north during 1994–2018
Subsurface nutrient stocks have increased in the western Arctic Ocean basin, but with larger nitrate deficit
Denitrifying activity on the marginal shelf might be enhanced as a result of climate change
This study uses a simulation method to explore how estuarine pH is affected by mixing between river water, anthropogenic CO2 enriched seawater, and by respiration. Three rivers with different levels ...of weathering products (Amazon, Mississippi, and St. Johns) are selected for this simulation. The results indicate that estuaries that receive low to moderate levels of weathering products (Amazon and St. Johns) exhibit a maximum pH decrease in the midsalinity region as a result of anthropogenic CO2 intrusion. This maximum pH decrease coincides with a previously unrecognized mid‐salinity minimum buffer zone (MBZ). In addition, water column oxygen consumption can further depress pH for all simulated estuaries. We suggest that recognition of the estuarine MBZs may be important for studying estuarine calcifying organisms and pH‐sensitive biogeochemical processes.
Key Points
Ocean acidification and O2 consumption can both lead to estuarine acidification
An previously undefined estuarine minimum buffer zone (MBZ) is demonstrated
Both estuarine carbonate chemistry and temperature affect the MBZ
The current outbreak of coronavirus disease-2019 (COVID-19) poses unprecedented challenges to global health
. The new coronavirus responsible for this outbreak-severe acute respiratory syndrome ...coronavirus 2 (SARS-CoV-2)-shares high sequence identity to SARS-CoV and a bat coronavirus, RaTG13
. Although bats may be the reservoir host for a variety of coronaviruses
, it remains unknown whether SARS-CoV-2 has additional host species. Here we show that a coronavirus, which we name pangolin-CoV, isolated from a Malayan pangolin has 100%, 98.6%, 97.8% and 90.7% amino acid identity with SARS-CoV-2 in the E, M, N and S proteins, respectively. In particular, the receptor-binding domain of the S protein of pangolin-CoV is almost identical to that of SARS-CoV-2, with one difference in a noncritical amino acid. Our comparative genomic analysis suggests that SARS-CoV-2 may have originated in the recombination of a virus similar to pangolin-CoV with one similar to RaTG13. Pangolin-CoV was detected in 17 out of the 25 Malayan pangolins that we analysed. Infected pangolins showed clinical signs and histological changes, and circulating antibodies against pangolin-CoV reacted with the S protein of SARS-CoV-2. The isolation of a coronavirus from pangolins that is closely related to SARS-CoV-2 suggests that these animals have the potential to act as an intermediate host of SARS-CoV-2. This newly identified coronavirus from pangolins-the most-trafficked mammal in the illegal wildlife trade-could represent a future threat to public health if wildlife trade is not effectively controlled.
The large areal extent of hypoxia in the northern Gulf of Mexico has been partially attributed to substantial nitrogen (N) loading from the Mississippi River basin, which is driven by multiple ...natural and human factors. The available water quality monitoring data and most of the current models are insufficient to fully quantify N load magnitude and the underlying controls. Here we use a process‐based Dynamic Land Ecosystem Model to examine how multiple factors (synthetic N fertilizer, atmospheric N deposition, land use changes, climate variability, and increasing atmospheric CO2) have affected the loading and delivery of total nitrogen (TN) consisting of ammonium and nitrate (dissolved inorganic N) and total organic nitrogen from the Mississippi River basin during 1901–2014. The model results indicate that TN export during 2000–2014 was twofold larger than that in the first decade of twentieth century: Dissolved inorganic N export increased by 140% dominated by nitrate; total organic nitrogen export increased by 53%. The substantial enrichment of TN export since the 1960s was strongly associated with increased anthropogenic N inputs (synthetic N fertilizer and atmospheric N deposition). The greatest export of TN was in the spring. Although the implementation of N reduction has been carried out over the past three decades, total N loads to the northern Gulf of Mexico have not decreased significantly. Due to the legacy effect from historical N accumulation in soils and riverbeds, a larger reduction in synthetic N fertilizer inputs as well as improved N management practices are needed to alleviate ocean hypoxia in the northern Gulf of Mexico.
Key Points
Over the period 1901‐2014, DIN and TON export from the Mississippi River basin increased by 85% and 60%, respectively. The Ohio River basin was largest contributor to the increase among seven subbasins
Synthetic N fertilizer application was the dominant contributor to increases in the export of DIN (70%) and TON (40%) since the 1970s
The highest DIN and TON export occurred in the spring, accounting for 39% and 36% of the total export from the MRB during 1990‐2014
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.
Plain Language Summary
Although both pH and calcium carbonate mineral saturation states (Ω) are good metrics for ocean acidification, in the global surface ocean their spatial patterns and seasonal cycles are often out of phase, which appears counter intuitive. To explain this, we separate pH and Ω changes into thermal and nonthermal components. Thermal components are mainly related to the temperature driven internal acid‐base equilibrium of seawater CO2 systems. Nonthermal components are the remaining changes, reflecting the effects of other non‐temperature processes such as air‐sea gas exchange, mixing and biology or a combination of these processes. We find that pH is controlled by the balance between thermal and nonthermal components, which are out of phase but comparable in magnitude, while Ω is almost always dominated by nonthermal components. These findings explain why surface ocean pH and Ω are often out of phase in spatial patterns and seasonal cycles. When pH is more controlled by nonthermal components than thermal components, pH and Ω will be in phase since their nonthermal components are intrinsically in phase. In contrast, when pH is more controlled by thermal components, pH and Ω will be out of phase because of the out‐of‐phase between thermal and nonthermal components of pH.
Key Points
pH is controlled by the balance of thermal components via acid‐base equilibrium and nonthermal components mainly via CO2 addition/removal
Carbonate saturation state (Ω) is dominated by nonthermal components mainly via external CO2 addition/removal
These differences explain why surface pH and Ω are often out of phase in spatial patterns and seasonal cycles
Ocean acidification (OA) defined as the decline of ocean pH and calcium carbonate saturation state (Ω) as a result of ocean uptake of CO2 from the atmosphere may have considerable negative impacts on ...global marine organisms and may substantially modify ocean biogeochemistry. However, as changes of pH and Ω are not conservative or linear with respect to ocean physical processes (e.g., mixing, temperature and pressure changes), the influences of anthropogenic CO2 uptake and ocean biogeochemical processes on OA rates cannot be easily identified. Here, we examine whether a composite property TA–DIC or the difference between total alkalinity (TA) and dissolved inorganic carbon (DIC), which is conservative to ocean mixing and is not sensitive to temperature and pressure changes, can be used for measuring OA rates and deciphering the underlying OA mechanisms in the global ocean as it in surface waters of several regional oceans. Based on Global Ocean Data Analysis Project Version 2 (GLODAPv2), we demonstrate using this property for measuring OA rates can be applied on a global ocean scale, except at low salinity e.g., < 20 and when TA–DIC is <~50 μmol kg−1, where the relationships of TA–DIC with pH and/or Ω are nonlinear. However, there are almost no limitations when using this property for deciphering the underlying OA mechanisms since the change of TA–DIC with time is relatively small on OA timescales of decades or more. Using TA–DIC, we can readily quantify the influences from freshwater inputs and upwelling on OA rates based on a two end-member mixing model. More importantly, through the Redfield ratio and apparent oxygen utilization, we can directly link biological influences to OA rates and conveniently quantify the biological modulation on OA rates. Therefore, we argue that using TA–DIC as a proxy for OA would provide a simple but powerful way of deciphering acidification mechanisms and predicting future development of acidification.
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•TA–DIC can be used for measuring OA and deciphering OA processes in global ocean.•TA–DIC is conservative to ocean mixing and insensitive to temperature and pressure.•Biological influences on OA rates can be directly linked via Redfield ratio and AOU.
Marine heatwaves (MHWs) are extremely warm ocean temperature events that significantly affect marine environments, but their effects on the coastal carbonate system are still uncertain. In this ...study, we systematically quantify MHWs' impacts on air‐sea carbon dioxide (CO2) flux anomalies (FCO2′) in the Mid‐Atlantic Bight (MAB) and South Atlantic Bight (SAB) from 1992 to 2020. During the longest MHW in both regions, oceanic CO2 uptake capabilities substantially decreased, primarily due to significant increases in the seawater partial pressure of CO2 (pCO2sea). For all cases, MHWs played a more significant role in driving pCO2sea changes in the MAB than the SAB, where non‐thermal drivers dominated pCO2sea variability. In the MAB, weakened wind speeds related to wintertime atmospheric perturbations increase ocean temperatures and pCO2sea, further reducing CO2 uptake during winter MHWs. This work is the first to connect extreme temperatures to coastal air‐sea CO2 fluxes. The reduction in CO2 absorption noted during MHWs in this study has important implications for coastal regions to act as continued sinks for excess CO2 emissions in the atmosphere.
Plain Language Summary
The transfer of carbon dioxide (CO2) between the atmosphere and ocean is sensitive to sea surface temperature (SST) changes because warmer SSTs increase the sea surface partial pressure of CO2 and reduce the ocean's ability to absorb CO2 from the atmosphere. It is, therefore, conceivable that marine heatwaves (MHWs), which are extremely warm ocean temperature events, could modify how carbon moves between the ocean and the atmosphere. This study provides the first attempt to evaluate the impacts of MHWs on the air‐sea CO2 flux (FCO2) anomalies along the US East Coast, encompassing the Mid‐Atlantic Bight (MAB) and South Atlantic Bight (SAB) during 1992–2020. Both regions experienced reduced CO2 absorption in response to the longest MHWs in each region. These extreme temperatures had a larger impact on CO2 absorption in the MAB compared to the SAB, where non‐temperature factors were more influential. The coastal ocean plays an important role in helping to mitigate human‐induced climate change by absorbing excess CO2 from the atmosphere. As such, the demonstrated reduced absorption of the ocean associated with MHWs in this study, which might also apply to other coastal locations, has vital implications for the efficiency of the ocean in offsetting global warming impacts.
Key Points
Marine heatwaves (MHWs) primarily generated positive sea surface pCO2 (pCO2sea) anomalies in the Mid‐Atlantic Bight (MAB) and South Atlantic Bight (SAB) but had a larger impact on air‐sea CO2 flux anomalies in the MAB
Reduced wind speeds amplified MHW contributions during CO2 sink months and counteracted them during CO2 source months
In the MAB, wintertime atmospheric perturbations related to zonal shifts in the jet stream produce slower wind speeds which aid in generating air‐sea heat flux type MHW events that ultimately reduce oceanic CO2 uptake
Seed size and weight are important factors that influence soybean yield. Combining the weighted gene co-expression network analysis (WGCNA) of 45 soybean accessions and gene dynamic changes in seeds ...at seven developmental stages, we identified candidate genes that may control the seed size/weight. Among these, a PLATZ-type regulator overlapping with 10 seed weight QTLs was further investigated. This zinc-finger transcriptional regulator, named as GmPLATZ, is required for the promotion of seed size and weight in soybean. The GmPLATZ may exert its functions through direct binding to the promoters and activation of the expression of cyclin genes and GmGA20OX for cell proliferation. Overexpression of the GmGA20OX enhanced seed size/weight in soybean. We further found that the GmPLATZ binds to a 32-bp sequence containing a core palindromic element AATGCGCATT. Spacing of the flanking sequences beyond the core element facilitated GmPLATZ binding. An elite haplotype Hap3 was also identified to have higher promoter activity and correlated with higher gene expression and higher seed weight. Orthologues of the GmPLATZ from rice and Arabidopsis play similar roles in seeds. Our study reveals a novel module of GmPLATZ-GmGA20OX/cyclins in regulating seed size and weight and provides valuable targets for breeding of crops with desirable agronomic traits.
Coastal hypoxia is an increasingly recognized environmental issue of global concern to both the scientific community and the general public. We assessed the relative contributions from marine and ...terrestrially sourced organic matter that were responsible for oxygen consumption in a well-studied seasonal coastal hypoxic zone, the East China Sea off the Changjiang Estuary. Our fieldwork was conducted in August 2011 during reinstatement of a subsurface hypoxia, when we observed a continuous decline of dissolved oxygen along with production of dissolved inorganic carbon resulting from organic carbon remineralization. On the basis of a three end-member mixing model and determinations of the stable isotopic compositions of dissolved inorganic carbon (δ(13)CDIC), the end product of particulate organic carbon (POC) degradation, we quantified the δ(13)C value of the remineralized organic carbon (δ(13)COCx), which was -18.5 ± 1.0‰. This isotopic composition was very similar to the δ(13)C of marine sourced POC produced in situ (-18.5 ± 0.3‰) rather than that of the terrestrially sourced POC (-24.4 ± 0.2‰). We concluded that marine-sourced organic matter, formed by eutrophication-induced marine primary production, was the dominant oxygen consumer in the subsurface hypoxic zone in the East China Sea off the Changjiang Estuary.
The carbon cycle of the coastal ocean is a dynamic component of the global carbon budget. But the diverse sources and sinks of carbon and their complex interactions in these waters remain poorly ...understood. Here we discuss the sources, exchanges and fates of carbon in the coastal ocean and how anthropogenic activities have altered the carbon cycle. Recent evidence suggests that the coastal ocean may have become a net sink for atmospheric carbon dioxide during post-industrial times. Continued human pressures in coastal zones will probably have an important impact on the future evolution of the coastal ocean's carbon budget.
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