• Energy Research
• 14. Life underwater close
• Oceanography close

Human activities, especially increased nutrient loads that set in motion a cascading chain of events related to eutrophication, accelerate development of hypoxia (lower oxygen concentration) in many areas of the world's coastal ocean. Climate changes and extreme weather events may modify hypoxia. Organismal and fisheries effects are at the heart of the coastal hypoxia issue, but more subtle regime shifts and trophic interactions are also cause for concern. The chemical milieu associated with declining dissolved oxygen concentrations affects the biogeochemical cycling of oxygen, carbon, nitrogen, phosphorus, silica, trace metals, and sulfide as observed in water column processes, shifts in sediment biogeochemistry, and increases in carbon, nitrogen, and sulfur, as well as shifts in their stable isotopes, in recently accumulated sediments.

Human activities, especially increased nutrient loads that set in motion a cascading chain of events related to eutrophication, accelerate development of hypoxia (lower oxygen concentration) in many areas of the world's coastal ocean. Climate changes and extreme weather events may modify hypoxia. Organismal and fisheries effects are at the heart of the coastal hypoxia issue, but more subtle regime shifts and trophic interactions are also cause for concern. The chemical milieu associated with declining dissolved oxygen concentrations affects the biogeochemical cycling of oxygen, carbon, nitrogen, phosphorus, silica, trace metals, and sulfide as observed in water column processes, shifts in sediment biogeochemistry, and increases in carbon, nitrogen, and sulfur, as well as shifts in their stable isotopes, in recently accumulated sediments.

Owing to anthropogenic-induced acidification, surface waters of the high latitudes are projected to become persistently undersaturated with respect to aragonite as early as mid-century. Seasonal aragonite undersaturation in surface and shallow subsurface waters of some northern polar seas has already been observed. Calcified marine organisms, including thecosomatous pteropods, foraminifers, cold-water corals, sea urchins, molluscs, and coralline algae, make up significant components of the rich communities in high latitudes, and they are thought to be at risk with increasing ocean acidification. Over the next decades, trends of rising temperatures and species invasions coupled with progressive ocean acidification are expected to increasingly influence both planktonic and benthic marine communities of Antarctica and the Arctic. The rate and magnitude of these changes underscore the urgent need for increased efforts in ocean acidity research and monitoring in polar and subpolar seas.

Owing to anthropogenic-induced acidification, surface waters of the high latitudes are projected to become persistently undersaturated with respect to aragonite as early as mid-century. Seasonal aragonite undersaturation in surface and shallow subsurface waters of some northern polar seas has already been observed. Calcified marine organisms, including thecosomatous pteropods, foraminifers, cold-water corals, sea urchins, molluscs, and coralline algae, make up significant components of the rich communities in high latitudes, and they are thought to be at risk with increasing ocean acidification. Over the next decades, trends of rising temperatures and species invasions coupled with progressive ocean acidification are expected to increasingly influence both planktonic and benthic marine communities of Antarctica and the Arctic. The rate and magnitude of these changes underscore the urgent need for increased efforts in ocean acidity research and monitoring in polar and subpolar seas.

Shifting to renewable energy is an important global challenge, and there are many technologies available to help reduce carbon dioxide emissions. Seawater air conditioning (SWAC) is a renewable ocean thermal energy technology that will soon be implemented in Honolulu, Hawaii, on the island of Oahu. The SWAC system will operate by using cool water from 500 m depth in a heat exchange system and then will release this nutrient-rich water back into the ocean at a shallower depth of 100–140 m. The introduction of a plume of warmed (but still relatively cool) deep seawater has unknown impacts on the tropical marine environment. Possible impacts include increases in primary production, changes in water chemistry and turbidity, and changes in the local food web. We used moored instruments and shipboard profiling to describe oceanographic parameters at the future SWAC effluent site. Parameters varied with the M2 internal tide, and denser water was correlated with higher nitrate, lower oxygen, and lower chlorophyll a (correlation coefficients 0.55, –0.58, and –0.75, respectively). The nitrate concentrations in the plume will be >30.0 µmol kg–1, while ambient concentrations range from <2.0–9.8 µmol kg–1. Irradiance levels at the effluent depth are sufficient to support net photosynthesis, and the effluent’s location in the pycnocline could lead to rapid horizontal advection of the plume and expansion of the spatial scale of impacts. These baseline data provide an understanding of pre-impact conditions at the future SWAC site and will enable a more accurate environmental assessment. A comprehensive and well-resolved environmental monitoring effort during SWAC operation will be necessary to quantify and understand these impacts.

Shifting to renewable energy is an important global challenge, and there are many technologies available to help reduce carbon dioxide emissions. Seawater air conditioning (SWAC) is a renewable ocean thermal energy technology that will soon be implemented in Honolulu, Hawaii, on the island of Oahu. The SWAC system will operate by using cool water from 500 m depth in a heat exchange system and then will release this nutrient-rich water back into the ocean at a shallower depth of 100–140 m. The introduction of a plume of warmed (but still relatively cool) deep seawater has unknown impacts on the tropical marine environment. Possible impacts include increases in primary production, changes in water chemistry and turbidity, and changes in the local food web. We used moored instruments and shipboard profiling to describe oceanographic parameters at the future SWAC effluent site. Parameters varied with the M2 internal tide, and denser water was correlated with higher nitrate, lower oxygen, and lower chlorophyll a (correlation coefficients 0.55, –0.58, and –0.75, respectively). The nitrate concentrations in the plume will be >30.0 µmol kg–1, while ambient concentrations range from <2.0–9.8 µmol kg–1. Irradiance levels at the effluent depth are sufficient to support net photosynthesis, and the effluent’s location in the pycnocline could lead to rapid horizontal advection of the plume and expansion of the spatial scale of impacts. These baseline data provide an understanding of pre-impact conditions at the future SWAC site and will enable a more accurate environmental assessment. A comprehensive and well-resolved environmental monitoring effort during SWAC operation will be necessary to quantify and understand these impacts.

The Ross Sea, the most productive region in the Antarctic, reaches farther south than any body of water in the world. While its food web is relatively intact, its oceanography, biogeochemistry, and sea ice coverage have been changing dramatically, and likely will continue to do so in the future. Sea ice cover and persistence have been increasing, in contrast to the Amundsen-Bellingshausen sector, which has resulted in reduced open water duration for its biota. Models predict that as the ozone hole recovers, ice cover will begin to diminish. Currents on the continental shelf will likely change in the coming century, with a projected intensification of flow leading to altered deep ocean ventilation. Such changes in ice and circulation will lead to altered plankton distributions and composition, but it is difficult at present to predict the nature of these changes. Iron and irradiance play central roles in regulating phytoplankton production in the Ross Sea, but the impacts of oceanographic changes on the biogeochemistry of iron are unclear. Unlike other Southern Ocean regions, where continental shelves are very narrow and Antarctic krill dominates the herbivorous fauna, the broad shelf of the Ross Sea is dominated by crystal krill and silverfish, which are the major prey items for higher trophic levels. At present, the Ross Sea is considered to be one of the most species-rich areas of the Southern Ocean and a biodiversity "hotspot" due to its heterogeneous habitats. Despite being among the best-studied regions in the entire Southern Ocean, accurate predictions of the impacts of climate change on the oceanography and ecology of the Ross Sea remain fraught with uncertainty.