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Biogeochemical Feature Subcomponent (WC)

Unit name Description
Benthic Boundary Layer The layer formed at the interface between the lower water column and the benthic substrate.
Boundary Layer Layer formed at the interface between water and another water mass (or solid interface) where frictional shear forces on water motion cause exponential damping of movement with proximity to the interface.
Chlorophyll Maximum A feature in deeper water columns (often in the ocean), where phytoplankton production is locally high at depths along a surface of nutrient (nitrate) entrainment from lower-water layers.
Chlorophyll Minimum A layer of low chlorophyll—and hence phytoplankton—concentration (relative to adjacent waters) due to highly concentrated grazing activity.
Drifting Fine Woody Debris Aggregations of floating or suspended fine woody material such as small tree branches, husks or fibrous seeds, with a median particle size < 64 millimeters.
Drifting Herbaceous Debris Floating or suspended detached, decaying herbaceous plant matter such as leaves, forbs or grasses, including deciduous leaves or needles, palm leaves, seagrass debris, <i>Spartina</i> debris.
Drifting Trees Floating or suspended large dead trees or very large branches, with a median particle size of greater than 4,096 millimeters.
Drifting Woody Debris Floating or suspended detached large branches with a median particle size of 64 millimeters to < 256 millimeters such as Mangrove branches, coconut rafts.
Euphotic Zone The zone of the water column that is sufficiently illuminated for photosynthesis to occur.
Halocline The zone of rapid salinity change with depth in the water column, often separating two layers of different, homogeneous salinity. As the density of water changes with salinity, the halocline presents a barrier to vertical circulation and enhances water column stability
Lens A homogeneous parcel of water that—by composition—maintains coherence within water of different properties. Often a freshwater lens will sit perched atop saline ocean waters for long periods.
Lysocline The depth in the ocean at which calcium dissolution increases due to increased pressure. This depth is around 4,000 meters in the Pacific Ocean and 5,000 meters in the Atlantic Ocean, owing to differences in temperature and chemistry. Below this depth, the precipitation of calcium carbonate decreases rapidly to the point where no calcite is deposited.
Marine Snow Aggregation A concentration of organic material in the ocean water column. Composed of a mix of mineral, dead organic materials, and—sometimes—a rich microbial community. In this feature small particles aggregate through attractive ionic forces and then begin to fall through the water column.
Microlayer Any extremely thin layer of material, nutrients, organisms or specific properties that exists on or in the water column. The microlayer can be a surface film or at depth and often refers to a microbial film.
Nepheloid Layer Layer of water that contains a high concentration of silt and sediment—usually at the benthic-water column interface. This layer can be nearly a fluid mud. In the deep oceans, the layer can be hundreds of meters thick; in shallower waters with less fine sediments, it can be much thinner (only a few centimeters in places) or absent. Thickness is determined by substrate composition and current shear.
Neustonic Layer Layer of biota that lives at the surface of the water. These organisms are either positively buoyant, maintain position by taking advantage of surface tension, or live on other biotic or abiotic material. Epineuston floats atop the water, hyponeuston lives just under the surface.
Nutrient Maximum A layer or region in the water column that has high concentrations of a particular nutrient or nutrients due either to biological transformation or to abiotic factors such as advection or entrainment from adjacent water masses.
Nutrient Minimum A layer in the ocean where net nutrient accumulation is at a minimum, often due to a locus of high biological activity drawing down nutrient stocks.
Nutricline The zone of rapid nutrient change with depth in the water column, often as a result of entrainment of water from a lower depth that is higher in concentration of a particular nutrient. The nutricline can be a rich source of a limiting nutrient and hence, the site of intense microbial or photosynthetic activity.
Oxygen Maximum A layer in the ocean where oxygen concentration is at a minimum, often due to a locus of high respiratory activity, notably microbial.
Oxygen Minimum Region in the water column where oxygen is reduced (relative to surrounding waters) due to high respiration rates, usually associated with high concentrations of organic matter.
Oxycline Zone in the water column where oxygen concentration changes rapidly with depth, often as a result of biological or abiotic processes that consume oxygen. Deep, bottom water that contains no photosynthetic organisms—yet receives much deposited organic matter—can generate both high respiration rates and extremely low oxygen concentrations. The transition layer between hypoxic bottom water and oxygenated surface water is the oxycline.
Sea Foam Sea foam is produced by turbulent mixing and agitation of surface waters, enhanced by high concentrations of dissolved organic matter (DOM).
Seep Area on the ocean bottom where fluid slowly emerges. Cold seeps are usually at the continental margins; waters in these seeps are often highly concentrated in minerals and dissolved gases, such as hydrogen sulfide, methane, and hydrogen. Cold-fluid seeps and oil seeps are sources of energy for chemoautotrophic communities of bacteria and archaea, which in turn support communities of clams, mussels and vestimentiferan tubeworms.
Surface Film Thin layer of materials and biota that exist on the surface of the water, often only a few microns thick. The surface film can contain a rich microbial community that consumes the material that concentrated in the film. Dissolved Organic Carbon (DOC) is concentrated up to five times in the surface microlayer. These films are often aggregated and concentrated at frontal convergences of two water masses and can lead to formation of a rich community that feeds on the material.
Surface Mixed Layer The layer of water at the ocean surface that is mixed by wind. Water of homogeneous density is easily mixed to a depth determined by the intensity of wind shear and density of the water. Often wind mixing of the surface occurs to the pycnocline depth where density increases rapidly. The mixed layer depth is an important determinant of the extent and intensity of photosynthetic production as plankton cells are mixed through the vertical light gradient.
Thermocline The zone of rapid temperature change with depth in the water column, often separating two layers of different, homogeneous temperature. As the density of water changes with temperature, the thermocline presents a barrier to vertical circulation and enhances water column stability.
Turbidity Maximum Region in an estuary where turbidity is high, due to concentration of particulates in the water column. This occurs as a result of the increasing ionic strength of the water from the introduction of salt in the downstream direction (generally at around areas with a salinity of 5), which causes particle aggregation. This process is enhanced by the mixing regime particular to this upper estuary region, in which countercurrent flows from the salt wedge are entrained into the seaward-flowing, upper-water layer. As particles settle out of the upper layer, they are carried upstream in the lower layer and so circulate within a zone of maximum turbidity.