Beschreibung: Highlights: • The epoch of the Anthropocene, a period during which human activity has been the dominant influence on climate and the environment, has witnessed a decline in oxygen concentrations and an expansion of oxygen-depleted environments in both coastal and open ocean systems since the middle of the 20th century. • This review paper provides a synthesis of system-specific drivers of low oxygen in a range of case studies representing marine systems in the open ocean, on continental shelves, in enclosed seas and in the coastal environment. • Identification of similar and contrasting responses within and across system types and corresponding oxygen regimes is shown to be informative both in understanding and isolating key controlling processes and provides a sound basis for predicting change under anticipated future conditions. • Case studies were selected to achieve a balance in system diversity and global coverage. • Each case study describes system attributes, including the present-day oxygen environment and known trends in oxygen concentrations over time. • Central to each case study is the identification of the physical and biogeochemical processes that determine oxygen concentrations through the tradeoff between ventilation and respiration. • Spatial distributions of oxygen and time series of oxygen data provide the opportunity to identify trends in oxygen availability and have allowed various drivers of low oxygen to be distinguished through correlative and causative relationships. • Deoxygenation results from a complex interplay of hydrographic and biogeochemical processes and the superposition of these processes, some additive and others subtractive, makes attribution to any particular driver challenging. • System-specific models are therefore required to achieve a quantitative understanding of these processes and of the feedbacks between processes at varying scales. Abstract: The epoch of the Anthropocene, a period during which human activity has been the dominant influence on climate and the environment, has witnessed a decline in oxygen concentrations and an expansion of oxygen-depleted environments in both coastal and open ocean systems since the middle of the 20th century. This paper provides a review of system-specific drivers of low oxygen in a range of case studies representing marine systems in the open ocean, on continental shelves, in enclosed seas and in the coastal environment. Identification of similar and contrasting responses within and across system types and corresponding oxygen regimes is shown to be informative both in understanding and isolating key controlling processes and provides a sound basis for predicting change under anticipated future conditions. Case studies were selected to achieve a balance in system diversity and global coverage. Each case study describes system attributes, including the present-day oxygen environment and known trends in oxygen concentrations over time. Central to each case study is the identification of the physical and biogeochemical processes that determine oxygen concentrations through the tradeoff between ventilation and respiration. Spatial distributions of oxygen and time series of oxygen data provide the opportunity to identify trends in oxygen availability and have allowed various drivers of low oxygen to be distinguished through correlative and causative relationships. Deoxygenation results from a complex interplay of hydrographic and biogeochemical processes and the superposition of these processes, some additive and others subtractive, makes attribution to any particular driver challenging. System-specific models are therefore required to achieve a quantitative understanding of these processes and of the feedbacks between processes at varying scales.

Beschreibung: In June 1985, a focused study was initiated to assess the spatial and temporal extent, intensity, and potential causes of oxygen depletion in the northern Gulf of Mexico. Hypoxic bottom waters were studied along two transects (one off Cat Island Pass near Cocodrie and one off Belle Pass off Port Fourchon) in the Mississippi River Delta Bight area. Eight 2-day cruises were conducted aboard the R/V R.J. Russell or the R/V Pelican along these two transects between mid-June and mid-October. Sampling was most intense (bi-weekly) from mid-June through early September. A reduced sampling scheme (4 stations along the Cat Island Pass transect) was continued through the end of the year. In addition, two shelf-wide cruises were conducted from the Mississippi River to the Texas border during July and September.

Beschreibung: Related data report: http://aquaticcommons.org/26970/

Beschreibung: In June 1985, a focused study was initiated to assess the spatial and temporal extent, intensity, and potential causes of oxygen depletion in the northern Gulf of Mexico. Two shelf-wide, quasi-synoptic cruises were conducted from the Mississippi River to the Texas border during mid-July and early September, 1985. Cruises were conducted aboard the R/V Pelican on 15-20 July and 10-13 September. Stations were occupied along ten transects in 5 to 80 m water depth. Stations for Pelican Cruise I extended farther offshore and farther to the west than those for Pelican Cruise II. In addition to these shelf-wide cruises, hypoxic bottom waters were studied more frequently along two transects in the Mississippi River Delta Bight area.

Beschreibung: Related data report: http://aquaticcommons.org/26966/

Beschreibung: In June 1985, a focused study was initiated to assess the spatial and temporal extent, intensity, and potential causes of oxygen depletion in the northern Gulf of Mexico. Hypoxic bottom waters were studied along two transects (one off Cat Island Pass near Cocodrie and one off Belle Pass near Port Fourchon). The number of transects was reduced to one in 1986 (Transect C off Cat Island Pass) and the number of sample periods increased. Sixteen cruises were conducted aboard the R/V Acadiana or the R/V Pelican between late January and mid-November, 1986. Sampling was most intense (bi-weekly) from mid-April through late September. A reduced sampling scheme (four stations) was followed for the first two cruises. In addition a shelf-wide cruise was conducted from the Mississippi River to the Texas border during July, 1986.

Beschreibung: Related data report: http://aquaticcommons.org/26996/

Beschreibung: In June 1985, a focused study was initiated to assess the spatial and temporal extent, intensity, and potential causes of oxygen depletion in the northern Gulf of Mexico. Hypoxic bottom waters were studied along two transects (one off Cat Island Pass near Cocodrie and one off Belle Pass near Port Fourchon). These cruises were continued in 1986 but on a single transect (see LUMCON Data Report No. 6). In addition, a shelf-wide cruise was conducted from the Mississippi River to the Texas border during July, 1986. Stations occupied during this cruise were similar to those sampled during shelf-wide cruises in 1985. The intent of these cruises was to provide comparative information on the temporal variability of oxygen-depleted bottom waters on the Louisiana shelf.The first part of the cruise was conducted on the R/V Acadiana between July 7 and July 10. Rough seas prevented continuation on the smaller ship. The remaining stations were sampled from on board the R/V Pelican between July 16 and July 17. While not synoptic in coverage, a few mid-depth stations were reoccupied during the second leg and hydrographic conditions were similar on the two dates.

Beschreibung: Related data report: http://aquaticcommons.org/26995/

Beschreibung: Since 1985, several research cruises were conducted by our research team to assess the spatial and temporal extent, intensity, and potential causes of oxygen depletion in the northern Gulf of Mexico. Hypoxic bottom waters were studied along two transects in and near the Mississippi River Delta Bight in 1985 and 1986. In addition, shelf-wide cruises were conducted from the Mississippi River to the Texas border during July of 1985, 1986, and 1987. These cruises have provided us with exhaustive information concerning the temporal and spatial variability associated with the phenomenon of hypoxia on the Louisiana shelf. It was not our intent to continue assessment-type cruises during 1988. Opportunities existed, however, in conjunction with other research cruises and the LUMCON summer program to re-occupy stations along Transect C off Cat Island Pass near Cocodrie. In addition, the drought conditions in the upper Mississippi River basin during the spring and summer of 1988 resulted in a significant reduction in the flow rate of the Mississippi River. We were therefore compelled to conduct a shelf-wide cruise during mid-summer of 1988 to document the hydrographic conditions of the Louisiana shelf under low flow conditions of the Mississippi River and to assess the effects of this low flow on the phenomenon of hypoxia.The cruises along Transect C were conducted on board the R/V Pelican as part of a research effort named LaSER for data in April and as part of the LUMCON summer program for the remainder. The shelf-wide cruise was conducted on board the R/V Acadiana from August 12 through August 16, 1988.

Beschreibung: Beginning in 1985, several research cruises were conducted by our research team to assess the spatial and temporal extent, intensity, and potential causes of oxygen depletion in the northern Gulf of Mexico. Hypoxic bottom waters were studied along two transects in and near the Mississippi River Delta Bight in 1985 and 1986. In addition, shelf-wide cruises were conducted from the Mississippi River to the Texas border during July of both years. The intent of these cruises was to provide comparative information on the temporal variability of oxygen-depleted bottom waters on the Louisiana shelf.The bi-weekly cruises along the southeastern Louisiana shelf were discontinued in 1987. A shelf-wide cruise, however, was conducted in July, 1987 to continue the studies of temporal variability on the Louisiana shelf. The cruise was conducted on the R/V Pelican from July 1 through July 5.