Numerical models of ocean biogeochemistry are relied upon to make projections about the impact of climate change on marine resources and test hypotheses regarding the drivers of past changes in ...climate and ecosystems. In large areas of the ocean, iron availability regulates the functioning of marine ecosystems and hence the ocean carbon cycle. Accordingly, our ability to quantify the drivers and impacts of fluctuations in ocean ecosystems and carbon cycling in space and time relies on first achieving an appropriate representation of the modern marine iron cycle in models. When the iron distributions from 13 global ocean biogeochemistry models are compared against the latest oceanic sections from the GEOTRACES program, we find that all models struggle to reproduce many aspects of the observed spatial patterns. Models that reflect the emerging evidence for multiple iron sources or subtleties of its internal cycling perform much better in capturing observed features than their simpler contemporaries, particularly in the ocean interior. We show that the substantial uncertainty in the input fluxes of iron results in a very wide range of residence times across models, which has implications for the response of ecosystems and global carbon cycling to perturbations. Given this large uncertainty, iron fertilization experiments based on any single current generation model should be interpreted with caution. Improvements to how such models represent iron scavenging and also biological cycling are needed to raise confidence in their projections of global biogeochemical change in the ocean.
Key Points
First intercomparison of 13 global iron models highlights key challenges in reproducing iron data
Wide uncertainty in iron input fluxes, which results in poorly constrained residence times
Reducing uncertainty in scavenging and biological cycling is a priority
The biological carbon pump (BCP) stores ∼1,700 Pg C from the atmosphere in the ocean interior, but the magnitude and direction of future changes in carbon sequestration by the BCP are uncertain. We ...quantify global trends in export production, sinking organic carbon fluxes, and sequestered carbon in the latest Coupled Model Intercomparison Project Phase 6 (CMIP6) future projections, finding a consistent 19 to 48 Pg C increase in carbon sequestration over the 21st century for the SSP3-7.0 scenario, equivalent to 5 to 17% of the total increase of carbon in the ocean by 2100. This is in contrast to a global decrease in export production of –0.15 to –1.44 Pg C y
–1
. However, there is significant uncertainty in the modeled future fluxes of organic carbon to the deep ocean associated with a range of different processes resolved across models. We demonstrate that organic carbon fluxes at 1,000 m are a good predictor of long-term carbon sequestration and suggest this is an important metric of the BCP that should be prioritized in future model studies.
A more insightful view of iron in glacial systems requires consideration of iron speciation and mineralogy, the potential for iron minerals to undergo weathering in ice-water environments, the impact ...of freezing on concentration and speciation, and potential for glacial delivery to undergo alteration during transport into the ocean. A size fractionation approach improves recognition of iron speciation by separating dissolved Fe (<0.2 or <0.45 μm) into soluble Fe (<0.02 μm) and colloidal/nanoparticulate Fe (0.02 to 0.2 or 0.45 μm). The ranges of soluble Fe concentrations in icebergs and meltwaters are similar (tens of nanomolar). The range of colloidal/nanoparticulate Fe concentrations in icebergs are an order of magnitude higher (hundreds of nanomolar) and up to thousands of nanomolar in meltwaters. The importance of particulate iron speciation in glacial sediments is also recognized by using carefully calibrated sequential extractions with ascorbic acid (FeA comprising fresh ferrihydrite which is potentially bioavailable) and dithionite (FeD comprising all remaining (oxyhydr)oxide Fe). Iceberg and glacier sediments contain lower concentrations of FeA (0.032 ± 0.024 and 0.042 ± 0.059 wt. %) than meltwater suspended sediments (FeA 0.12 ± 0.09 wt. %). Glacier sediments also contain low concentrations of FeD (0.060 ± 0.036) but concentrations of FeD are comparable in iceberg and meltwater sediments (0.38 ± 0.24 wt. % compared to 0.31 ± 0.09 wt.%). Reactions in ice-water systems produce potentially bioavailable Fe(II) and ferrihydrite by pyrite oxidation, iron mineral dissolution (aided by low pH and organic complexes) and reduction (aided by UV radiation). Some icebergs contain high concentrations of FeA (>0.1 wt. %) which represent samples in which the on-going transformation of ferrihydrite to goethite/hematite is incomplete. Numerical models of freezing in subglacial systems show that the nanomolar levels of soluble Fe in icebergs cannot be achieved solely by freezing, and must indicate the presence of nanoparticulate Fe and/or iron desorbed from ice or sediments during melting. Models of freezing effects in sea ice show that nanomolar levels of soluble Fe are achievable because high concentrations of hydroxide and chloride ions maintain dissolved iron as soluble complexes. Delivery of iron through fjords is temporally and spatially variable due to circulation patterns, mixing of different sources, and aggregation through salinity gradients.
We present an extension to the carbon-centric Grid Enabled Integrated Earth system model (cGEnIE) that explicitly accounts for the growth and interaction of an arbitrary number of plankton species. ...The new package (ECOGEM) replaces the implicit, flux-based parameterisation of the plankton community currently employed, with explicitly resolved plankton populations and ecological dynamics. In ECOGEM, any number of plankton species, with ecophysiological traits (e.g. growth and grazing rates) assigned according to organism size and functional group (e.g. phytoplankton and zooplankton) can be incorporated at runtime. We illustrate the capability of the marine ecology enabled Earth system model (EcoGEnIE) by comparing results from one configuration of ECOGEM (with eight generic phytoplankton and zooplankton size classes) to climatological and seasonal observations. We find that the new ecological components of the model show reasonable agreement with both global-scale climatological and local-scale seasonal data. We also compare EcoGEnIE results to the existing biogeochemical incarnation of cGEnIE. We find that the resulting global-scale distributions of phosphate, iron, dissolved inorganic carbon, alkalinity, and oxygen are similar for both iterations of the model. A slight deterioration in some fields in EcoGEnIE (relative to the data) is observed, although we make no attempt to re-tune the overall marine cycling of carbon and nutrients here. The increased capabilities of EcoGEnIE in this regard will enable future exploration of the ecological community on much longer timescales than have previously been examined in global ocean ecosystem models and particularly for past climates and global biogeochemical cycles.
Estimates of glacial sediment delivery to the oceans have been derived from fluxes of meltwater runoff and iceberg calving, and their sediment loads. The combined total (2900
Tg
yr
−1) of the ...suspended sediment load in meltwaters (1400
Tg
yr
−1) and the sediment delivered by icebergs (1500
Tg
yr
−1) are within the range of earlier estimates. High-resolution microscopic observations show that suspended sediments from glacial meltwaters, supraglacial, and proglacial sediments, and sediments in basal ice, from Arctic, Alpine, and Antarctic locations all contain iron (oxyhydr)oxide nanoparticles, which are poorly crystalline, typically ∼5
nm in diameter, and which occur as single grains or aggregates that may be isolated or attached to sediment grains. Nanoparticles with these characteristics are potentially bioavailable. A global model comparing the sources and sinks of iron present as (oxyhydr)oxides indicates that sediment delivered by icebergs is a significant source of iron to the open oceans, beyond the continental shelf. Iceberg delivery of sediment containing iron as (oxyhydr)oxides during the Last Glacial Maximum may have been sufficient to fertilise the increase in oceanic productivity required to drawdown atmospheric CO
2 to the levels observed in ice cores.
We model iceberg flow paths from the Eurasian Ice Sheet, and the associated meltwater production and sedimentation rates within the Norwegian–Greenland Sea during the last glaciation. Results from a ...numerical ice sheet model, an atmospheric general circulation model and an ocean general circulation model are collated and used to provide iceberg production rate, wind field and surface current forcings to an iceberg trajectory model. The iceberg model then determines how icebergs issuing from the Eurasian Ice Sheet travel across the ocean and eventually melt. In addition the release of iceberg sediments is also predicted. The results show that iceberg trajectories are complex and that common features of iceberg movement are clustering in zones of convergence and exit into the North Atlantic through the Iceland–Faeroes Channel. Eurasian icebergs do not penetrate into the interior of the Arctic Ocean. The gathering of icebergs produces a complex meltwater pattern that does not follow the conceptual idea of decreasing meltwater production with distance from the ice sheet margin. Sedimentation results are compared with the meltwater configuration and are found to be a poor indicator of past zones of iceberg melt, with zones of sedimentation extending significantly less far.
Climate change, the COVID-19 pandemic, environmental destruction, and attitudes to death in high-income countries have similar roots—our delusion that we are in control of, and not part of, nature. ...Palliative care can provide better outcomes for patients and carers at the end of life, leading to improved quality of life, often at a lower cost, but attempts to influence mainstream health-care services have had limited success and palliative care broadly remains a service-based response to this social concern. Income, education, gender, race, ethnicity, sexual orientation, and other factors influence how much people suffer in death systems and the capacity they possess to change them. The five principles are: the social determinants of death, dying, and grieving are tackled; dying is understood to be a relational and spiritual process rather than simply a physiological event; networks of care lead support for people dying, caring, and grieving; conversations and stories about everyday death, dying, and grief become common; and death is recognised as having value. The five principles are: the social determinants of death, dying, and grieving are tackled; dying is understood to be a relational and spiritual process rather than simply a physiological event; networks of care lead support for people dying, caring, and grieving; conversations and stories about everyday death, dying, and grief become common; and death is recognised as having value.
Lancet Commission on the Value of Death Smith, Richard; Blazeby, Jane; Bleakley, Tracey ...
The Lancet (British edition),
10/2018, Volume:
392, Issue:
10155
Journal Article
PDF
