Marine dissolved organic matter (DOM) presents key thermodynamic properties that are not yet fully constrained. Here, we report the distribution of binding sites occupied by protons (i.e., proton ...affinity spectra) and parametrize the median intrinsic proton binding affinities (log
) and heterogeneities (
), for DOM samples extracted from the North Atlantic. We estimate that 11.4 ± 0.6% of C atoms in the extracted marine DOM have a functional group with a binding site for ionic species. The log
of the most acidic groups was larger (4.01-4.02 ± 0.02) than that observed in DOM from coastal waters (3.82 ± 0.02), while the chemical binding heterogeneity parameter increased with depth to values (
= 0.666 ± 0.009) ca. 10% higher than those observed in surface open ocean or coastal samples. On the contrary, the log
for the less acidic groups shows a difference between the surface (10.01 ± 0.08) and deep (9.22 ± 0.35) samples. The latter chemical groups were more heterogeneous for marine than for terrestrial DOM, and
decreased with depth to values of 0.28 ± 0.03. Binding heterogeneity reflects aromatic carbon compounds' persistence and accumulation in diverse, low-abundance chemical forms, while easily degradable low-affinity groups accumulate more uniformly in the deep ocean.
Oceanic dissolved inorganic carbon (TC) is the largest pool of carbon that substantially interacts with the atmosphere on human timescales. Oceanic TC is increasing through uptake of anthropogenic ...carbon dioxide (CO2), and seawater pH is decreasing as a consequence. Both the exchange of CO2 between the ocean and atmosphere and the pH response are governed by a set of parameters that interact through chemical equilibria, collectively known as the marine carbonate system. To investigate these processes, at least two of the marine carbonate system's parameters are typically measured – most commonly, two from TC, total alkalinity (AT), pH, and seawater CO2 fugacity (fCO2; or its partial pressure, pCO2, or its dry-air mole fraction, xCO2) – from which the remaining parameters can be calculated and the equilibrium state of seawater solved. Several software tools exist to carry out these calculations, but no fully functional and rigorously validated tool written in Python, a popular scientific programming language, was previously available. Here, we present PyCO2SYS, a Python package intended to fill this capability gap. We describe the elements of PyCO2SYS that have been inherited from the existing CO2SYS family of software and explain subsequent adjustments and improvements. For example, PyCO2SYS uses automatic differentiation to solve the marine carbonate system and calculate chemical buffer factors, ensuring that the effect of every modelled solute and reaction is accurately included in all its results. We validate PyCO2SYS with internal consistency tests and comparisons against other software, showing that PyCO2SYS produces results that are either virtually identical or different for known reasons, with the differences negligible for all practical purposes. We discuss insights that guided the development of PyCO2SYS: for example, the fact that the marine carbonate system cannot be unambiguously solved from certain pairs of parameters. Finally, we consider potential future developments to PyCO2SYS and discuss the outlook for this and other software for solving the marine carbonate system. The code for PyCO2SYS is distributed via GitHub (https://github.com/mvdh7/PyCO2SYS, last access: 23 December 2021) under the GNU General Public License v3, archived on Zenodo (Humphreys et al., 2021), and documented online (https://pyco2sys.readthedocs.io/en/latest/, last access: 23 December 2021).
The high-latitude oceans are key areas of carbon and heat exchange between
the atmosphere and the ocean. As such, they are a focus of both modern
oceanographic and palaeoclimate research. However, ...most palaeoclimate
proxies that could provide a long-term perspective are based on calcareous
organisms, such as foraminifera, that are scarce or entirely absent in
deep-sea sediments south of 50∘ S in the Southern Ocean and north
of 40∘ N in the North Pacific. As a result, proxies need to be
developed for the opal-based organisms (e.g. diatoms) found at these high
latitudes, which dominate the biogenic sediments recovered from these
regions. Here we present a method for the analysis of the boron (B) content
and isotopic composition (δ11B) of diatom opal. We apply it for
the first time to evaluate the relationship between seawater pH, δ11B and B concentration (B) in the frustules of the diatom
Thalassiosira weissflogii, cultured across a range of carbon dioxide partial pressure (pCO2) and
pH values. In agreement with existing data, we find that the B
of the cultured diatom frustules increases with increasing pH (Mejía et al.,
2013). δ11B shows a relatively well defined negative trend with
increasing pH, completely distinct from any other biomineral previously
measured. This relationship not only has implications for the magnitude of
the isotopic fractionation that occurs during boron incorporation into opal,
but also allows us to explore the potential of the boron-based proxies for
palaeo-pH and palaeo-CO2 reconstruction in high-latitude marine
sediments that have, up until now, eluded study due to the lack of suitable
carbonate material.
The global mean surface temperature and partial pressure of carbon dioxide (CO2) are increasing both in the atmosphere and ocean. Oceanic CO2 uptake causes a decline in pH called ocean acidification ...(OA), which also alters other biologically important carbonate system variables such as carbonate mineral saturation states. Here, we discuss how a “temperature buffering” effect chemically links the rates of warming and OA at a more fundamental level than is often appreciated, meaning that seawater warming could mitigate some of the adverse biological impacts of OA. In a global mean sense, the rate of warming relative to the CO2 increase can be quantified by the climate sensitivity (CS), the exact value of which is uncertain. It may initially appear that a greater CS would therefore reduce the negative influence of OA. However, the dependence of the rate of CO2 increase on the CS could enhance, nullify or even reverse the temperature buffering effect, depending upon the future trajectory of anthropogenic CO2 emissions. Regional deviations from the global mean seawater temperature and CO2 uptake trends could modulate local responses to OA. For example, mitigation of OA impacts through temperature buffering could be particularly effective in the Arctic Ocean, where the surface seawater warming rate is greater than the global mean, and the aqueous CO2 concentration might increase more slowly than elsewhere. Some carbonate system variables are more strongly affected than others, highlighting the need to develop a mechanistic understanding of precisely which variables are important to each biogeochemical process. Temperature buffering of the marine carbonate system should be taken into account when designing experiments to determine marine species and ecosystem responses to warming and OA, in order that their results accurately reflect future conditions, and therefore can generate realistic predictions when applied to Earth system models.
Previous work has not led to a clear understanding of the causes of spatial pattern in global surface ocean dissolved inorganic carbon (DIC), which generally increases polewards. Here, we revisit ...this question by investigating the drivers of observed latitudinal gradients in surface salinity-normalized DIC (nDIC) using the Global Ocean Data Analysis Project version 2 (GLODAPv2) database. We used the database to test three different hypotheses for the driver producing the observed increase in surface nDIC from low to high latitudes. These are (1) sea surface temperature, through its effect on the CO2 system equilibrium constants, (2) salinity-related total alkalinity (TA), and (3) high-latitude upwelling of DIC- and TA-rich deep waters. We find that temperature and upwelling are the two major drivers. TA effects generally oppose the observed gradient, except where higher values are introduced in upwelled waters. Temperature-driven effects explain the majority of the surface nDIC latitudinal gradient (182 of the 223 µmol kg−1 increase from the tropics to the high-latitude Southern Ocean). Upwelling, which has not previously been considered as a major driver, additionally drives a substantial latitudinal gradient. Its immediate impact, prior to any induced air–sea CO2 exchange, is to raise Southern Ocean nDIC by 220 µmol kg−1 above the average low-latitude value. However, this immediate effect is transitory. The long-term impact of upwelling (brought about by increasing TA), which would persist even if gas exchange were to return the surface ocean to the same CO2 as without upwelling, is to increase nDIC by 74 µmol kg−1 above the low-latitude average.
The stable isotopic composition of particulate organic carbon
(δ13CPOC) in the surface waters of the global ocean can
vary with the aqueous CO2 concentration (CO2(aq)) and affects
the trophic ...transfer of carbon isotopes in the marine food web. Other
factors such as cell size, growth rate and carbon concentrating mechanisms
decouple this observed correlation. Here, the variability in δ13CPOC is investigated in surface waters across the south
subtropical convergence (SSTC) in the Atlantic Ocean, to determine carbon
isotope fractionation (εp) by phytoplankton and the
contrasting mechanisms of carbon uptake in the subantarctic and subtropical
water masses. Our results indicate that cell size is the primary determinant
of δ13CPOC across the Atlantic SSTC in summer. Combining
cell size estimates with CO2 concentrations, we can accurately estimate
εp within the varying surface water masses in this region.
We further utilize these results to investigate future changes in
εp with increased anthropogenic carbon availability. Our
results suggest that smaller cells, which are prevalent in the subtropical
ocean, will respond less to increased CO2(aq) than the larger cells
found south of the SSTC and in the wider Southern Ocean. In the subantarctic
water masses, isotopic fractionation during carbon uptake will likely
increase, both with increasing CO2 availability to the cell, but also
if increased stratification leads to decreases in average community cell
size. Coupled with decreasing δ13C of CO2(aq) due to
anthropogenic CO2 emissions, this change in isotopic fractionation and
lowering of δ13CPOC may propagate through the marine food
web, with implications for the use of δ13CPOC as a tracer
of dietary sources in the marine environment.
This study is the first to our knowledge to examine associations of survey-reported dietary supplement use with medical record diagnoses, rather than retrospective self-reported supplement use at the ...time of the medical encounter or case reports of adverse events. Dietary supplement (DS) use and adverse events associations in US Navy and Marine Corps personnel remains unknown. This study assessed associations of DS use in active duty (AD) personnel with ICD-9-CM diagnostic codes from outpatient medical encounters from the Military Health System Data Repository (MDR).
This cross-sectional investigation used a one-time survey of DS use among AD conducted August through December 2014. Survey data were matched to MDR data accessed in September 2016, and associations between the survey responses and diagnoses were analyzed. Statistical significance was set at alpha level 0.005, and 99.5% confidence intervals (CIs) were calculated. MDR data were matched with survey results for 1,708 personnel. Multivariable logistic regression analyses examined whether use of specific classes of supplements was associated with disease.
Results revealed significant associations between vitamin supplement use and ICD-9-CM-diagnosed diseases of the nervous system (odds ratio OR: 1.72, 99.5% CI: 1.11-2.68) and diseases of the musculoskeletal system and connective tissue (OR: 1.59, 99.5% CI: 1.17-2.17). Joint health supplement category use was associated with diseases of the musculoskeletal system and connective tissue (OR: 1.81, 99.5% CI: 1.12-2.94) and injury and poisoning (OR: 1.82, 99.5% CI: 1.10-3.04).
The percentages of service members with diseases in specific ICD-9-CM diagnostic categories were similar to those reported in other studies using military medical data. There is a greater prevalence of dietary supplement use by the service members who participated in this survey compared with the general population, with 73% of US Navy and Marine Corps personnel reporting use of dietary supplements one or more times per week compared to the estimated 50% of all Americans currently using some form of dietary supplement. The DoD ensures the optimal readiness, performance, and health of its military service members, thus future longitudinal evaluation of dietary supplement use by this population will test the preliminary findings of this study.
Mercury (Hg) in seawater is subject to interconversions via (photo)chemical and (micro)biological processes that determine the extent of dissolved gaseous mercury (DGM) (re)emission and the ...production of monomethylmercury. We investigated Hg speciation in the South Atlantic Ocean on a GEOTRACES cruise along a 40°S section between December 2011 and January 2012 (354 samples collected at 24 stations from surface to 5250 m maximum depth). Using statistical analysis, concentrations of methylated mercury (MeHg, geometric mean 35.4 fmol L−1) were related to seawater temperature, salinity, and fluorescence. DGM concentrations (geometric mean 0.17 pmol L−1) were related to water column depth, concentrations of macronutrients and dissolved inorganic carbon (DIC). The first-ever observed linear correlation between DGM and DIC obtained from high-resolution data indicates possible DGM production by organic matter remineralization via biological or dark abiotic reactions. DGM concentrations projected from literature DIC data using the newly discovered DGM–DIC relationship agreed with published DGM observations.
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•Dissolved gaseous mercury can be calculated from modeled dissolved inorganic carbon.•Modeled dissolved gaseous mercury agrees well with worldwide observations.•Dissolved gaseous mercury is related to depth and macronutrients concentrations.
Accumulation of anthropogenic CO2 is significantly altering ocean chemistry. A range of biological impacts resulting from this oceanic CO2 accumulation are emerging, however, the mechanisms ...responsible for observed differential susceptibility between organisms and across environmental settings remain obscure. A primary consequence of increased oceanic CO2 uptake is a decrease in the carbonate system buffer capacity, which characterizes the system's chemical resilience to changes in CO2, generating the potential for enhanced variability in pCO2 and the concentration of carbonate CO32−, bicarbonate HCO3−, and protons H+ in the future ocean. We conducted a meta‐analysis of 17 shipboard manipulation experiments performed across three distinct geographical regions that encompassed a wide range of environmental conditions from European temperate seas to Arctic and Southern oceans. These data demonstrated a correlation between the magnitude of natural phytoplankton community biological responses to short‐term CO2 changes and variability in the local buffer capacity across ocean basin scales. Specifically, short‐term suppression of small phytoplankton (<10 μm) net growth rates were consistently observed under enhanced pCO2 within experiments performed in regions with higher ambient buffer capacity. The results further highlight the relevance of phytoplankton cell size for the impacts of enhanced pCO2 in both the modern and future ocean. Specifically, cell size‐related acclimation and adaptation to regional environmental variability, as characterized by buffer capacity, likely influences interactions between primary producers and carbonate chemistry over a range of spatio‐temporal scales.
We evidenced a correlation between the magnitude of natural phytoplankton community biological responses to short‐term CO2 changes and variability in the local buffer capacity across ocean basin scales. Specifically, short‐term suppression of small phytoplankton (<10 µm) net growth rates were consistently observed under enhanced pCO2 within experiments performed in regions with higher ambient buffer capacity. The results further highlight the relevance of phytoplankton cell size for the impacts of enhanced pCO2 in both the modern and future ocean.
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