The open ocean is a vital player in Earth's biogeochemistry. drive , converting inorganic carbon to organic matter. , especially by , phosphorus, and , controls productivity. The transports organic matter from surface to deep waters.
Ocean circulation shapes . brings nutrient-rich deep waters to the surface, while ventilates the ocean interior. Climate change impacts ocean biogeochemistry through acidification, deoxygenation, and shifts in primary production. The ocean acts as a crucial carbon sink, absorbing CO2 through solubility and biological pumps.
Open Ocean Biogeochemical Processes
Biogeochemical processes in open oceans
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Enhanced stratification reduces vertical mixing and ventilation
Oxygen minimum zones expand, threatening marine ecosystems
Alters biogeochemical cycles, particularly nitrogen and phosphorus
Changes in primary production
Shifts phytoplankton community structure (smaller species favored)
Alters nutrient availability and limitation patterns
Impacts biological pump efficiency and carbon export
Regional variations expected (increases in polar regions, decreases in tropics)
Ocean's role as global carbon sink
Ocean carbon sink
Solubility pump dissolves CO2 in cold, dense waters
Biological pump exports organic carbon to deep ocean
Ocean absorbs ~25% of anthropogenic CO2 emissions annually
Changes in ocean circulation affect CO2 uptake and storage
Alterations in marine ecosystems impact carbon cycling
Potential release of methane hydrates amplifies warming
Ocean-atmosphere interactions
driven by partial pressure differences
(ENSO) influences CO2 fluxes
Long-term changes in ocean heat content affect CO2 solubility
Ocean carbon sink may saturate, reducing uptake capacity
Tipping points in ocean-climate system (thermohaline circulation shutdown)
Uncertainties in climate models and biogeochemical feedbacks complicate predictions
Key Terms to Review (24)
Air-sea gas exchange: Air-sea gas exchange refers to the process by which gases are transferred between the atmosphere and the ocean's surface. This process is crucial for regulating atmospheric concentrations of gases like carbon dioxide and oxygen, significantly influencing ocean carbon dynamics and impacting acidification as well as broader open ocean biogeochemical cycles.
Antarctic Bottom Water: Antarctic Bottom Water (AABW) is a dense, cold water mass that forms in the Southern Ocean, particularly around Antarctica, as surface waters cool and sink. This process creates one of the most significant contributors to global thermohaline circulation, influencing oceanic currents and nutrient distribution in the open ocean, ultimately affecting global climate and marine ecosystems.
Biological pump: The biological pump is a crucial process in the ocean that describes how biological activity, particularly by phytoplankton, facilitates the transfer of carbon dioxide (CO2) from the atmosphere to the deep ocean. This process plays a key role in regulating global climate by sequestering carbon and cycling nutrients, thus impacting marine ecosystems and biogeochemical cycles in the open ocean.
Carbon cycle feedbacks: Carbon cycle feedbacks refer to the processes that either amplify or dampen the effects of carbon emissions on the climate system. These feedbacks can be positive, where an increase in carbon leads to further increases in carbon, or negative, where increases lead to decreases. They play a crucial role in understanding how the carbon cycle interacts with climate change and influence patterns of biogeochemical processes in various ecosystems, particularly in the open ocean.
Carbon dioxide solubility pump: The carbon dioxide solubility pump is a process by which carbon dioxide (CO2) is absorbed from the atmosphere into the ocean and subsequently transported to deeper waters. This occurs as CO2 dissolves in seawater, driven by differences in partial pressure between the air and ocean surface, leading to a reduction of atmospheric CO2 levels and helping to regulate global climate.
Carbon Sequestration: Carbon sequestration is the process of capturing and storing atmospheric carbon dioxide (CO2) to mitigate climate change. This process can occur naturally through biological systems or artificially through technology, significantly impacting carbon reservoirs, fluxes, and overall climate dynamics.
Deep Water Formation: Deep water formation refers to the process by which surface waters, typically in high-latitude regions, become dense enough to sink to the ocean's depths, contributing to the global thermohaline circulation. This process plays a critical role in regulating ocean temperatures and nutrient distribution, influencing marine ecosystems and biogeochemical cycles.
El Niño-Southern Oscillation: El Niño-Southern Oscillation (ENSO) is a climate phenomenon characterized by variations in ocean temperatures and atmospheric conditions in the central and eastern Pacific Ocean. This oscillation consists of two main phases: El Niño, which brings warmer ocean temperatures, and La Niña, which brings cooler temperatures, both significantly impacting global weather patterns, marine ecosystems, and biogeochemical cycles in the open ocean.
Future Projections: Future projections refer to predictions about the future state of environmental conditions and processes based on current data and models. In the context of open ocean biogeochemistry, these projections are essential for understanding how changes in factors like temperature, carbon dioxide levels, and nutrient availability can affect marine ecosystems and global climate patterns over time.
Iron: Iron is a crucial trace metal that plays an essential role in various biogeochemical processes, particularly in the open ocean. It serves as a fundamental nutrient for phytoplankton, supporting primary production and influencing marine food webs. The availability of iron in oceanic waters often limits biological productivity, making it a key factor in understanding oceanic carbon cycling and nutrient dynamics.
Liebig's Law of the Minimum: Liebig's Law of the Minimum states that the growth of an organism is limited by the essential nutrient that is in the shortest supply relative to the needs of that organism. This principle emphasizes that an ecosystem's productivity is not solely determined by the abundance of resources but also by the availability of the least abundant resource necessary for growth, which plays a crucial role in biogeochemical cycles.
Nitrogen: Nitrogen is a colorless, odorless gas that makes up about 78% of the Earth's atmosphere and is an essential element for all living organisms, primarily because it is a key component of amino acids, proteins, and nucleic acids. In biogeochemical cycles, nitrogen undergoes various transformations, including fixation, mineralization, nitrification, and denitrification, which play vital roles in nutrient availability and ecosystem functioning.
North Atlantic Deep Water: North Atlantic Deep Water (NADW) is a deep ocean current that forms in the North Atlantic Ocean, characterized by its cold and dense water mass. It plays a crucial role in global ocean circulation and is essential for nutrient transport, impacting marine ecosystems and biogeochemical cycles in the open ocean. The formation of NADW occurs when warm, salty surface waters cool and sink, contributing to the thermohaline circulation, which influences climate and weather patterns across the globe.
Nutrient Distribution: Nutrient distribution refers to the spatial and temporal patterns in the availability and concentration of essential nutrients within the open ocean. This concept is crucial in understanding how nutrients like nitrogen, phosphorus, and iron are dispersed and recycled in marine environments, influencing primary productivity and the overall health of oceanic ecosystems. Variations in nutrient distribution can significantly impact food webs and biogeochemical cycles, highlighting the interconnectedness of biological and chemical processes in ocean systems.
Nutrient Limitation: Nutrient limitation occurs when the growth of organisms, particularly plants and phytoplankton, is restricted by the lack of essential nutrients in their environment. This concept is crucial in understanding ecosystem productivity and health, as certain nutrients, like nitrogen or phosphorus, can become scarce, impacting biological processes and overall ecosystem dynamics.
Ocean acidification: Ocean acidification refers to the process by which the ocean becomes more acidic due to increased absorption of carbon dioxide (CO2) from the atmosphere. This phenomenon has significant implications for marine ecosystems, carbonate chemistry, and global biogeochemical cycles.
Ocean deoxygenation: Ocean deoxygenation refers to the progressive decline in dissolved oxygen levels in ocean waters, primarily driven by human activities such as climate change, nutrient runoff, and overfishing. This phenomenon has significant implications for marine life and biogeochemical processes, impacting everything from the health of ecosystems to global carbon cycles.
Ocean's role as global carbon sink: The ocean's role as a global carbon sink refers to its ability to absorb and store carbon dioxide (CO2) from the atmosphere, significantly helping to regulate Earth's climate. This process is essential because it mitigates the greenhouse effect and helps maintain the planet's temperature by reducing atmospheric CO2 levels. Various oceanic processes, including biological uptake through photosynthesis and physical absorption of gases, contribute to the ocean's capacity to sequester carbon.
Oxygen minimum zones: Oxygen minimum zones (OMZs) are regions in the ocean where the concentration of dissolved oxygen is significantly lower than that of surrounding waters. These zones typically occur at depths between 200 and 1,500 meters, where biological and chemical processes deplete oxygen faster than it can be replenished. OMZs are important for understanding marine ecosystems and biogeochemical cycles, as they influence the distribution of marine life and the cycling of nutrients and organic matter.
PH Levels: pH levels measure the acidity or alkalinity of a solution on a scale from 0 to 14, with 7 being neutral. Understanding pH levels is crucial as they influence chemical reactions, biological processes, and the health of ecosystems in both terrestrial and aquatic environments, especially in the context of carbon dynamics and the impacts of acidification on marine life and soil chemistry.
Phytoplankton: Phytoplankton are microscopic, photosynthetic organisms that drift in the sunlit upper layers of oceans, seas, and freshwater bodies. They serve as the foundation of aquatic food webs and play a crucial role in biogeochemical cycles by converting sunlight into chemical energy through photosynthesis, which in turn supports a wide range of marine life.
Primary Production: Primary production refers to the process by which autotrophs, such as plants and phytoplankton, convert inorganic carbon (primarily CO₂) into organic compounds through photosynthesis or chemosynthesis. This process is crucial because it forms the foundation of the food web and affects nutrient cycling, energy flow, and the overall health of ecosystems.
Redfield Ratio: The Redfield Ratio is a reference ratio that describes the typical stoichiometric relationship between carbon, nitrogen, and phosphorus in marine phytoplankton and the organic matter they produce. This ratio is commonly represented as 106:16:1 for carbon, nitrogen, and phosphorus, respectively, and serves as a foundational concept in understanding nutrient cycling and interactions within various biogeochemical processes.
Upwelling: Upwelling is the process where deep, nutrient-rich waters rise to the surface, often due to wind patterns and ocean currents. This phenomenon plays a vital role in supporting marine ecosystems and enhancing productivity by bringing essential nutrients to the photic zone, where sunlight penetrates, allowing phytoplankton to thrive.