A grand challenge for ocean chemists in the years ahead lies in the need to tackle the chemical consequences of ocean warming with the same rigor and intensity that has been brought to bear on the ...physical chemistry of ocean acidification. For over 50 years ocean chemistry has been dominated by the study of pH‐dependent processes, but to address the biogeochemical impacts of ocean warming, we will need to rapidly advance the discipline of ocean chemical physics where temperature is the master variable and the basic unit is the Joule. Just as it would be impossible to understand the ocean CO2 system without awareness of the essential pH‐dependent CO2‐HCO3‐CO3 equilibria, so too is it impossible to describe ocean chemical physics without knowledge of the bimolecular structure of water. Water, and water in sea water, is composed of a complex of dominant hydrogen bonded forms, and the singlet molecular H2O species, in temperature‐controlled equilibrium and the ratio of these forms, can now be precisely determined. The physical properties of sea water are traditionally described by fitting an ad hoc collection of coefficients to experimental data. They are more accurately described as temperature and pressure perturbations of the underlying molecular equilibrium state. Ocean oxygen consumption rates are accurately described as an Arrhenius function, and not as an exponential function of depth as has been the tradition for over 50 years. We do not now have good correlation between ocean models and observed warming and oxygen declines, and full anoxia with the emergence of hydrogen sulfide over large regions of the ocean is possible. The parallel ocean invasions of heat and fossil fuel CO2 must be combined to estimate their full impact.
Plain Language Summary
The ocean absorbs some 93% of all greenhouse gas‐generated heat, and ocean warming is already creating observable impacts on marine life. To make reliable projections for the future, we cannot rely on Ptolemy‐like rules, built as something to match field observations, to apply in the years to come. Instead, we will need to apply the laws of chemical physics to calculate and predict the changes that ocean warming will have on the physical properties of sea water and the associated impacts on marine life. This includes treating water as a fluid with defined temperature‐ and pressure‐dependent chemical structures. Sea water is 96.5% water, and some 78–85% of water in the oceans has a form with a much higher molecular weight than the water molecule that typically comes to mind, with a single oxygen and two hydrogens. These varied structures are now directly relatable to the high heat capacity of water, why the speed of sound is faster in warmer water, and the viscosity of sea water that provides constraints on microbial motion. Microbial activity is a key driver to the amount of oxygen in different parts of the ocean, and if their activity is affected by increased warmth, it seems quite possible that large regions may exist with no oxygen at all. Marine life responds strongly to changing oxygen status. This is because both warmer waters can hold less oxygen, and because warming drives higher rates of microbial growth. Marine fisheries, and the great majority of all marine species, are already responding to these forces and are migrating toward cooler waters near the poles. Using known laws of science to connect chemistry, physics, and ocean warming would allow the ocean sciences to proceed on firmer footing and to improve future projections of the impact of ocean warming. The ocean is now experiencing the twinned invasions of heat and fossil fuel carbon dioxide that drive up its acid level. It is the combined impact of these two great waves, both resulting from our use of fossil fuels, that will be critical, and right now the correlations are not well known or examined.
Key Points
Ocean warming will increase rates of ocean oxygen consumption with impacts on marine life
Ocean heat capacity is directly related to water molecular structure
The basic discipline of chemical physics can be applied to these problems with considerable certainty
Calendar-dated tree-ring sequences offer an unparalleled resource for high-resolution paleoenvironmental reconstruction. Where such records exist for a few limited geographic regions over the last ...8,000 to 12,000 years, they have proved invaluable for creating precise and accurate timelines for past human and environmental interactions. To expand such records across new geographic territory or extend data for certain regions further backward in time, new applications must be developed to secure “floating” (not yet absolutely dated) tree-ring sequences, which cannot be assigned single-calendar year dates by standard dendrochronological techniques. This study develops two approaches to this problem for a critical floating tree-ring chronology from the East Mediterranean Bronze–Iron Age. The chronology is more closely fixed in time using annually resolved patterns of 14C, modulated by cosmic radiation, between 1700 and 1480 BC. This placement is then tested using an anticorrelation between calendardated tree-ring growth responses to climatically effective volcanism in North American bristlecone pine and the Mediterranean trees. Examination of the newly dated Mediterranean tree-ring sequence between 1630 and 1500 BC using X-ray fluorescence revealed an unusual calcium anomaly around 1560 BC. While requiring further replication and analysis, this anomaly merits exploration as a potential marker for the eruption of Thera.
There is a concerted global effort to digitize biodiversity occurrence data from herbarium and museum collections that together offer an unparalleled archive of life on Earth over the past few ...centuries. The Global Biodiversity Information Facility provides the largest single gateway to these data. Since 2004 it has provided a single point of access to specimen data from databases of biological surveys and collections. Biologists now have rapid access to more than 120 million observations, for use in many biological analyses. We investigate the quality and coverage of data digitally available, from the perspective of a biologist seeking distribution data for spatial analysis on a global scale. We present an example of automatic verification of geographic data using distributions from the International Legume Database and Information Service to test empirically, issues of geographic coverage and accuracy. There are over 1/2 million records covering 31% of all Legume species, and 84% of these records pass geographic validation. These data are not yet a global biodiversity resource for all species, or all countries. A user will encounter many biases and gaps in these data which should be understood before data are used or analyzed. The data are notably deficient in many of the world's biodiversity hotspots. The deficiencies in data coverage can be resolved by an increased application of resources to digitize and publish data throughout these most diverse regions. But in the push to provide ever more data online, we should not forget that consistent data quality is of paramount importance if the data are to be useful in capturing a meaningful picture of life on Earth.
For over 50 years, ocean scientists have oddly represented ocean oxygen consumption rates as a function of depth but not temperature in most biogeochemical models. This unique tradition or tactic ...inhibits useful discussion of climate change impacts, where specific and fundamental temperature-dependent terms are required. Tracer-based determinations of oxygen consumption rates in the deep sea are nearly universally reported as a function of depth in spite of their well-known microbial basis. In recent work, we have shown that a carefully determined profile of oxygen consumption rates in the Sargasso Sea can be well represented by a classical Arrhenius function with an activation energy of 86.5 kJ mol−1, leading to a Q10 of 3.63. This indicates that for 2°C warming, we will have a 29% increase in ocean oxygen consumption rates, and for 3°C warming, a 47% increase, potentially leading to large-scale ocean hypoxia should a sufficient amount of organic matter be available to microbes. Here, we show that the same principles apply to a worldwide collation of tracer-based oxygen consumption rate data and that some 95% of ocean oxygen consumption is driven by temperature, not depth, and thus will have a strong climate dependence. The Arrhenius/Eyring equations are no simple panacea and they require a non-equilibrium steady state to exist. Where transient events are in progress, this stricture is not obeyed and we show one such possible example.
This article is part of the themed issue ‘Ocean ventilation and deoxygenation in a warming world’.
The high heat capacity of seawater has been cited as why 93% of the heat trapped by anthropogenic greenhouse gases is absorbed by the ocean. Specific heats (CP) are closely tied to molecular weight. ...The mean molecular weight of pure water over the range 0–40 °C is 86.1–80.7 and 89.4–84.5 for seawater. Warming of water increases the kinetic energy of the molecules and induces breaking of hydrogen bonds (8.364 kJ/mol); both effects increase the volume of the fluid. Warming pure water from 0–10 °C increases the single H2O molecular form by 1.64%, accounting for 36.3% of the energy consumed. The specific heat of pure water is thus attributable (63.7%) to increasing the kinetic energy of the water, and (36.3%) to the energy required to break hydrogen bonds. For seawater, 34.7% of the energy goes to breaking hydrogen bonds while the rest (65.3%) is attributable to increasing the kinetic energy of the molecules.
Key Points
The specific heat of water and sea water is a function of the molecular structure governed by hydrogen bonding.
Warming water and sea water breaks hydrogen bonds and releases single H2O molecules accounting for 36% of the heat absorbed.
The molecular weight of water ranges from 86 to 81 from 0 to 40 degrees C accounting for the remaining 64% of the specific heat.
Ocean ventilation and deoxygenation in a warming world: introduction and overview Shepherd, John G.; Brewer, Peter G.; Oschlies, Andreas ...
Philosophical transactions - Royal Society. Mathematical, Physical and engineering sciences/Philosophical transactions - Royal Society. Mathematical, physical and engineering sciences,
09/2017, Letnik:
375, Številka:
2102
Journal Article
Recenzirano
Odprti dostop
Changes of ocean ventilation rates and deoxygenation are two of the less obvious but important indirect impacts expected as a result of climate change on the oceans. They are expected to occur ...because of (i) the effects of increased stratification on ocean circulation and hence its ventilation, due to reduced upwelling, deep-water formation and turbulent mixing, (ii) reduced oxygenation through decreased oxygen solubility at higher surface temperature, and (iii) the effects of warming on biological production, respiration and remineralization. The potential socio-economic consequences of reduced oxygen levels on fisheries and ecosystems may be far-reaching and significant. At a Royal Society Discussion Meeting convened to discuss these matters, 12 oral presentations and 23 posters were presented, covering a wide range of the physical, chemical and biological aspects of the issue. Overall, it appears that there are still considerable discrepancies between the observations and model simulations of the relevant processes. Our current understanding of both the causes and consequences of reduced oxygen in the ocean, and our ability to represent them in models are therefore inadequate, and the reasons for this remain unclear. It is too early to say whether or not the socio-economic consequences are likely to be serious. However, the consequences are ecologically, biogeochemically and climatically potentially very significant, and further research on these indirect impacts of climate change via reduced ventilation and oxygenation of the oceans should be accorded a high priority.
This article is part of the themed issue ‘Ocean ventilation and deoxygenation in a warming world’.
Limits to Marine Life Brewer, Peter G.; Peltzer, Edward T.
Science (American Association for the Advancement of Science),
04/2009, Letnik:
324, Številka:
5925
Journal Article
Recenzirano
Ocean "dead zones" devoid of aerobic life are likely to grow as carbon dioxide concentrations rise.
Clathrate hydrates in nature Hester, Keith C; Brewer, Peter G
Annual review of marine science,
01/2009, Letnik:
1
Journal Article
Recenzirano
Scientific knowledge of natural clathrate hydrates has grown enormously over the past decade, with spectacular new findings of large exposures of complex hydrates on the sea floor, the development of ...new tools for examining the solid phase in situ, significant progress in modeling natural hydrate systems, and the discovery of exotic hydrates associated with sea floor venting of liquid CO2. Major unresolved questions remain about the role of hydrates in response to climate change today, and correlations between the hydrate reservoir of Earth and the stable isotopic evidence of massive hydrate dissociation in the geologic past. The examination of hydrates as a possible energy resource is proceeding apace for the subpermafrost accumulations in the Arctic, but serious questions remain about the viability of marine hydrates as an economic resource. New and energetic explorations by nations such as India and China are quickly uncovering large hydrate findings on their continental shelves.
The influence of ocean acidification in deep-sea ecosystems is poorly understood but is expected to be large because of the presumed low tolerance of deep-sea taxa to environmental change. We used a ...newly developed deep-sea free ocean CO2 enrichment (dp-FOCE) system to evaluate the potential consequences of future ocean acidification on the feeding behavior of a deep-sea echinoid, the sea urchin, Strongylocentrotus fragilis. The dp-FOCE system simulated future ocean acidification inside an experimental enclosure where observations of feeding behavior were performed. We measured the average movement (speed) of urchins as well as the time required (foraging time) for S. fragilis to approach its preferred food (giant kelp) in the dp-FOCE chamber (−0.46 pH units) and a control chamber (ambient pH). Measurements were performed during each of 4 trials (days −2, 2, 24, 27 after CO2 injection) during the month-long period when groups of urchins were continuously exposed to low pH or control conditions. Although urchin speed did not vary significantly in relation to pH or time exposed, foraging time was significantly longer for urchins in the low-pH treatment. This first deep-sea FOCE experiment demonstrated the utility of the FOCE system approach and suggests that the chemosensory behavior of a deep-sea urchin may be impaired by ocean acidification.
The smell of hydrogen sulfide upon recovery of deep sea cores from areas of reducing sediments is familiar to most ocean scientists and is simple testimony to the problem of dissolved gas loss during ...core recovery and processing. For this reason methods of in situ measurement of sulfide and other gases are keenly sought, and both microelectrode and spectroscopic measurements have been widely used. We report here on the use of a robust 50cm long titanium pore water probe combined with a laser Raman sensing system for in situ measurement of the sulfide concentration and sulfide speciation status of deep sea sediment pore waters. Uniquely the Raman signal spectroscopically senses and simultaneously resolves both the H2S (υ1 2592 Δcm−1) and HS− (υ1 2573 Δcm−1) species. We have calibrated the Raman response factors as a function of pH and found that the Raman cross section for HS− is a factor of 1.563 greater than for the H2S form. We have carried out stepwise profiling of the pore water chemistry (CH4, SO42−, H2S, HS−) of highly reducing sediments in the Santa Monica Basin and from the combined sulfide species we can assess total dissolved sulfide. Since the ratio of HS−:H2S is a well-defined function of pH with the pK for this equilibrium being close to 7.0, and since the pH of many sediment pore waters is also close to 7 then the observed HS−:H2S ratio provides an elegant pH sensitive “dye”. We have solved the required Raman-equilibrium relationships and show that the in situ pH of sulfide rich pore waters can be determined rapidly and directly from these observations. Several field examples are provided.
•ROV mounted laser Raman spectrometer is used to make in situ measurements.•Laboratory measurements were used to calibrate both total sulfide and pH determinations.•Measurements were made at 10cm intervals to a maximum depth (in sediment) of 60cm.•Pore-water pH ranged from 7.5 to 8.0 near the surface to as low as 7.0 at depth.•Precision of the pH measurements was on the order of ±0.02 pH.
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