|Benthic Boundary Layer
||The layer formed at the interface between the lower water column and the benthic substrate.
||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.
||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
||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>
||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.
||The zone of the water column that is sufficiently illuminated for photosynthesis to
||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
||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.
||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.
||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.
||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.
||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.
||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.
||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.
||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.
||A layer in the ocean where oxygen concentration is at a minimum, often due to a locus
of high respiratory activity, notably microbial.
||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
||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
||Sea foam is produced by turbulent mixing and agitation of surface waters, enhanced
by high concentrations of dissolved organic matter (DOM).
||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.
||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.
||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.
||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.