Oxygen Minimum Zones (OMZs) may expand in the future as a result of the decline in oxygen concentrations in the ocean (e.g., Stramma et al. 2010). The downward flux of particulate organic matter (POM) from the euphotic zone via the biological carbon pump (BCP) is critical to transfer carbon to the ocean’s interior. Export efficiency and flux attenuation impact the vertical distribution of...
One of the impacts of climate change on the oceans is the reduction in dissolved oxygen concentrations in seawater (termed ‘deoxygenation’) as less oxygen dissolves in warmer waters and enhanced oceanic stratification reduces oxygen supply to the ocean interior. Expansion and intensification of the tropical oxygen minimum zones (OMZs) as a result of ocean deoxygenation in turn may affect the...
Global biogeochemical ocean models are now routinely used to estimate the potential increase of tropical and subtropical oxygen minimum zones (OMZs). However, to date many of these models do not accurately represent the current extent and location of these. Beside the representation of physical processes, biogeochemical model parameters might be of importance for a model's fit to observed...
Observations indicate an expansion of oxygen minimum zones over the past 50 years, likely related to ongoing global deoxygenation. Here we analyze the processes and feedbacks, which contribute to global deoxygenation on millennial timescales using an Earth system model of intermediate complexity for a business-as-usual CO2 emission scenario. Particularly, we discuss how terrestrial weathering...
Benthic trace metal fluxes in the oxygen minimum zone off Peru
A. PLASS1*, F. SCHOLZ1, C. SCHLOSSER1, A. W. DALE1, E. P. ACHTERBERG1, S. SOMMER1
1GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstraße 1-3, 24148 Kiel, Germany
(*correspondence: aplass@geomar.de)
Iron and several other trace metals (e.g. cobalt, zinc, cadmium) are essential micronutrients, required for the...
Shelf sediments in oxygen minimum zones (OMZs) are a major contributor of iron (Fe) and other bioessential trace metals to offshore waters. Future changes in metal fluxes are projected as a result of expansion of OMZs, potentially having important biogeochemical impacts on adjacent ocean systems. Resolving the processes in OMZs that determine trace metal release from sediments, stabilisation...
The Benguela region is an eastern boundary upwelling system exhibiting seasonally anoxic conditions. The region receives elemental inputs from aeolian, benthic and riverine sources, such as that from the Congo and Orange Rivers. Continental shelves, at the land-ocean interface, play an important role in marine primary productivity by supplying trace elements such as iron (Fe) and cobalt (Co)...
Atmospheric deposition of trace elements and nutrients are crucial determinants of ocean biogeochemistry, providing a direct supply of essential macro- and micronutrients to surface seawaters. However, very few direct measurements exist to quantify aerosol trace element and nutrient input to remote oceanic regions. Fe is known to limit primary production across the Equatorial pacific and thus...
Nitrogen fixing cyanobacteria are autotrophic prokaryotes that require specific trace metals, such as iron (Fe), cobalt (Co), copper (Cu), molybdenum (Mo), manganese (Mn) and zinc (Zn), as cofactors in enzymes. Metalloenzymes regulate physiological processes that are key to life, such as photosynthesis, nitrogen fixation and respiration. Iron is the main limiting trace nutrient in the ocean,...
Upwelling associated with eastern boundary currents transports nutrients to sunlit surface waters, fuelling phytoplankton productivity. Phytoplankton growth rapidly depletes supplied nutrients such than one or more become limiting; the supply flux of the limiting nutrient(s) is therefore the proximal control on productivity. In this presentation the results of direct experimental tests in...
Dissolved iron (DFe) concentrations in oxygen minimum zones (OMZs) of Eastern Boundary Upwelling Systems are enhanced as a result of high supply rates from anoxic sediments. However, pronounced variaions in DFe concentraions in anoxic coastal waters of the Peruvian OMZ indicate that there are factors in addition to O2 availability that control the cycling of Fe. Our results show that...
Iron (Fe), Manganese (Mn) and Copper (Cu) are three redox active trace metals required for a range of critical biological processes in marine organisms. Iron is known as the essential in photosystem I, for its dust input and it being the limiting element in about 30% of the surface of the Ocean. Manganese is the active metal centre in several redox enzymes, most notably in photosystem II where...
The oxygen minimum zone (OMZ) in the eastern tropical South Pacific (ETSP) promotes the microbial loss of nitrogen from the water column accompanied by release of sediment bound phosphate. Consequently, subsurface water masses depleted in dissolved inorganic nitrogen and enriched in dissolved inorganic phosphorus (low N:P ratio) are upwelled to the surface layer off Peru. Geochemical tracer...
The largest uncertainty and inconsistency in global marine N2O emission estimate appear in the euphotic zone where physical disturbances prevents N2O accumulation if any. Here we presented high vertical resolution N2O profiles in the euphotic zone with distinctive peaks near the oxycline in the oligotrophic Western Pacific, where the maximum of Chl-a and nitrite appeared correspondingly....
The tropical Oxygen Minimum Zones (OMZs) are key regions of very low oxygen in today's ocean. Recent investigations have shown that the oxygen content of the global ocean is decreasing and OMZs are expanding, and the future ocean may experience significant shifts in nutrient cycling, strongly affecting the biological productivity in surface waters. Besides phosphate (PO4) and nitrate (NO3-),...
As a consequence of global warming oxygen saturations in will increase due to decreasing oxygen solubility and potential changes to biological and physical processes. There is strong observational evidence that deoxygenation has occurred over the last 50 years or so, at least in certain areas. When oxygen concentrations reach very low levels organic matter oxidation proceeds via...
Oxygen minimum zone (OMZ) sediments were identified as key regions for nitrogen loss as well as for recycling of reactive N species releasing high amounts of ammonium ($NH_4^+$) into the bottom water and thereby affecting the water column elemental ratios and processes. Despite this significance the response of benthic N-cycling in relation to variability in the bottom water redox scheme, i.e....
In this study, we present the results from an ex situ incubation experiment of sediment cores from the Peruvian oxygen minimum zone (750 m water depth). The motivation is to understand how the efficiency, timing and magnitude of nutrient recycling responds to lower levels of oxygen and nitrate in the water column. Three sediment cores (one control, two replicates) were incubated for 17 days on...
The northern Gulf of Mexico (nGOM) and the East China Sea (ECS) face similar physical drivers and anthropogenic stressors. Most importantly, both systems are strongly influenced by large rivers (the Mississippi and Changjiang) and intense eutrophication due to agriculture and population growth. Bottom water hypoxia and acidification appear to grow more severe in recent years in both systems...
Increased anthropogenic inputs of nitrogen and phosphorus from land have led to eutrophication of marine environments worldwide. Coastal systems can reduce the flux of nutrients from land to the open sea, thereby acting as a coastal filter. The key processes that remove nitrogen and phosphorus in coastal areas are denitrification and phosphorus burial [1]. Recent modeling of nutrient dynamics...
Hydrographic observations in the Cochin backwaters (CBW), southwest coast of India during the summer monsoon delineated the spreading of an unusually anoxic water mass in the bottom characterized by intense denitrification and formation of hydrogen sulphide, which have not been previously reported from any tropical estuaries. The coastal zone of western India experiences moderate upwelling...
Phosphorus (P) is a key nutrient for marine primary producers. River input is the most important source of P in the ocean while its main sink is burial in marine sediments. Low oxygen in the ocean can lead to enhanced regeneration of P relative to carbon during degradation of organic matter in the water column and in sediments. This process can act as a positive feedback on marine productivity...
The El Niño/Southern Oscillation (ENSO) is an irregularly periodic variation in winds and sea surface temperatures over the tropical eastern Pacific Ocean, affecting climate of much of the tropics and subtropics. Only recently model results suggested that both the warm (El Niño) and the cold phases (La Niña) of ENSO are affecting nitrogen processes such as denitrification in the oxygen minimum...
Anthropogenic warming is expected to drive oxygen (O$_2$) out of the ocean causing a massive perturbation of the nitrogen (N) cycle leading to increasing N removal and oceanic N$_2$O production via denitrification, which would trigger enhanced N$_2$ fixation. Our intermediate complexity Earth system model simulations reveal that N$_2$ fixation does not compensate the enhanced N loss due...
The marine biological response to atmospheric CO$_2$ concentration being reduced from a greenhouse to an icehouse climate shows a surprisingly symmetric hysteresis compared to when it is increased from an icehouse to a greenhouse climate. We equilibrate the University of Victoria Earth System Climate Model, at 280 and 1260 ppm atmospheric CO$_2$, then force it with a 1% per year increase (the...
Biotic processes in biogeochemical models are usually greatly oversimplified in the sense that they are represented by closure terms unrelated to the behaviour of the organisms involved. This applies to both Redfield models of primary production, which ignore the highly variable elemental stoichiometry of phytoplankton and Holling-type models of grazing, which are at odds with observed...