Oceanic dissolved oxygen has been observed to decrease over the past decades. Yet, the exact mechanisms leading to these changes and the relative role of natural and forced variability are not completely understood. Similarly, the time of emergence (ToE) of anthropogenic O2 trends from the “noise” caused by chaotic internal variability as well as naturally-forced variations, e.g., in response...
The extent and intensity of oxygen miminum zones (OMZs) along productive continental margins are tightly coupled to changes in ocean ventilation and biogeochemical feedbacks. The reconstruction of spatial and temporal changes of these parameters is crucial to understand the mechanisms driving marine redox conditions in the past. The application of redox-sensitive proxies like molybdenum (Mo)...
enter code here
Liebetrau V.1, Glock N.1,2, Eisenhauer A.1 and Vogts A.3
1 GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstr. 1–3, 24148 Kiel, Germany
2 Collaborative Research Center 754, Climate Biogeochemistry Interactions in the Tropical Ocean, Kiel University, Germany
3 IOW, Leibniz-Institute for Baltic Sea Research, Seestrasse 15, 18119 Rostock, Germany
Oceanic oxygen...
The Humboldt Current System (HCS) off Peru yields about 10% of the global fish catch, producing more fish per unit area than any other region in the world ocean. The current high productivity is fuelled by the upwelling of cold, nutrient-rich water from the oxygen minimum zone (OMZ). However, the potential impacts of climate change on upwelling dynamics and fish productivity as well as the...
Permanent oxygen deficiency in intermediate-depth waters is an important feature of the ocean. These water volumes are known as oxygen minimum zones (OMZ) and exhibit a high sensitivity to climate variability providing feedbacks on climate drivers. Over the last decade, several studies have reported global ocean deoxygenation trends since the 1960s and a consequent OMZ expansion. However,...
The abrupt change to a regime of high productivity with nutrient-rich and low-oxygen concentration waters on the Eastern Tropical Pacific since the end of the Little Ice Age (LIA) promoted the development of an intense Oxygen Minimum Zone (OMZ) that allows the preservation of carbonates at the seafloor. Calcareous benthic foraminifera dominates foraminiferal faunas in most OMZ realms and...
Deoxygenation is recognized with growing concern in the modern Baltic Sea and results in increasing areas of hypoxia ([O2]<1.4 ml/l). The Baltic Sea has been highly prone to deoxygenation during the Holocene. Our goal is to study how the extent and severity of hypoxia in the region have varied over the Holocene from 7.5 ka BP to present: to achieve this, we use high accumulation rate sediment...
During the past 125 million years, the Earth experienced a series of major global warming episodes, including the Early Aptian Selli-Event (OAE1a) the Cenomanian-Turonian Boundary Event (OAE2), the Paleocene-Eocene Thermal Maximum and the Miocene Climate Optimum (MCO). All these episodes were associated with fundamental disturbances of the global carbon cycle, expressed as prominent excursions...
The late Miocene (~11.6 to 5.3 million years ago) represents a geologically recent interval of relative global warmth that was marked by profound environmental change in both terrestrial and marine ecosystems. This period offers the opportunity to assess the sensitivity of the Earth’s climate to changing boundary conditions, such as ice volume and radiative forcing, on a warmer-than-modern...
Presently, productivity and oxygenation of the Arabian Sea are governed by the upwelling generated along the Oman Margin. Upwelling in this area is strongly related to the modern monsoonal regime and tectonic configuration of the region, which was established during the Early and Middle Miocene (~23.0 to 11.7 Ma).
Recent new records from the north Western Indian Ocean (Maldives) and...
Deoxygenation and productivity of the Late Cretaceous ocean were studied using the UVic earth system model. Simulations were performed at 4 different atmospheric pCO2 values (500 ppm, 1200 ppm, 1800 ppm, 2200 ppm) using a state-of-the-art reconstruction of paleogeography and ocean basin configuration. Consistent with the proxy record, the model predicts low oxygen conditions for the proto...
Major perturbations of the global carbon cycle are globally imprinted as prominent carbon isotope excursions (CIEs) in Mesozoic sedimentary successions. These CIEs have been linked to the widespread enhancement of primary productivity in ocean basins, which strongly impacted the oxygenation of subsurface water masses. We investigate changes in redox-conditions in a 265 m continuous succession...
Recent observations of the modern ocean show that the ocean is experiencing progressive deoxygenation. While it is likely that ancient climate events experienced similar variations, our current proxies lack the resolution to definitively fingerprint non-sulfidic, low oxygen bottom waters. Throughout the Phanerozoic there are numerous climatic perturbations with associated extinction events...
The Eastern Tropical South Pacific (ETSP) oxygen minimum zone (OMZ) is one of the largest regional OMZs in the global ocean. At multidecadal to millennial scales, the intensity and extension of this OMZ is modulated by changes of the Walker circulation, which control the thermocline depth –and thus productivity and respiration– in the ETSP, as well as the subsurface ventilation associated to...
The controls on dissolved oxygen are complex, involving oxygen saturation concentrations, ocean circulation, air-sea gas exchange and the rate of organic matter respiration. Marine sediment records of oxygenation during the last ice age provide a means to gauge the relative importances of these mechanisms, as well as the response of the marine ecosystem, under climate forcings that are...
Suboxic to anoxic conditions were existing in large parts of the Mediterranean basin during the deposition of Sapropel S1 (ca. 12 to 6 ka BP). If the general mechanism for the development of a basin-wide paleo-OMZ have been intensively investigated, the relationships between flood seasonality and the strength and extend of the OMZ remain elusive. Here we propose to use a unique 5 m-thick...
Our understanding of how marine microbial processes and nitrogen cycling will respond to future increases in atmospheric CO2 and global temperature, as well as ocean acidification and deoxygenation, is very limited. This is largely due to a lack of proxies that can register ocean biogeochemical processes in sedimentary archives during past transitions to warmer climates. We present biomarker...
Anthropogenic impacts are perturbing the global nitrogen cycle via warming effects and
pollutant sources such as chemical fertilizers and burning of fossil fuels. Nitrate is one of the main limiting nutrients in the modern ocean and nitrate fertilization might contribute to the ongoing ocean deoxygenation. The quantitative reconstruction of past reactive nitrogen inventories is indispensable...
Global warming and its effect on the stratification and oxygen solubility of the Ocean is leading to declines in the marine oxygen inventory, with potentially catastrophic consequences for ecosystem and habitat sustainability and marine productivity. Total oxygen inventory has already declined by 2% since 1960 and deoxygenation is predicted to accelerate over the rest of the century (Keeling...
Multiproxy paleoenvironmental reconstructions are crucial in order to improve our understanding of the nutrient rich, high productivity environments, such as the Peruvian upwelling system, in relation with the currently changing climate. In this study we present compilation of multiproxy results focusing on the relationship between benthic and pelagic environment in relation with a strong...
Oxygen minimum zones (OMZ) have expanded in all tropical oceans during the last decades resulting in habitat contraction and considerable changes in marine biogeochemistry. However, it is still an open question as to how the magnitude and temporal changes in oceanic dissolved oxygen of the last few decades compare to the natural variability on longer timescales and how local and remote...
The formation of Antarctic Bottom Water (AABW) around the Antarctic margin ventilates the deep ocean and contributes to the global overturning circulation system. Oceanographic observations in recent decades have revealed an accelerated warming and freshening of AABW, which suggest that significant changes in the southern limb of the global circulation system are likely, in response to...