Marine eco

Photic zone

The upper layer of the ocean where enough light penetrates for photosynthesis to occur.

Mixed layer

The relatively well-mixed surface layer where temperature, salinity, and density are relatively uniform.

Pycnocline

A layer where seawater density changes rapidly with depth, creating a barrier to vertical mixing.

Thermocline

A layer where temperature changes rapidly with depth.

Stratification

Vertical layering of the ocean caused by differences in density that limit vertical mixing.

Upwelling

Movement of deep, cold, nutrient-rich water toward the surface.

Downwelling

Movement of surface water downward into deeper parts of the ocean.

Nutricline

A depth range where nutrient concentrations increase rapidly with depth.

Primary productivity

The rate at which primary producers create organic matter from inorganic materials, primarily through photosynthesis.

Gross Primary Productivity (GPP)

The total amount of organic carbon produced through photosynthesis before subtracting respiration.

Net Primary Productivity (NPP)

Primary production remaining after autotrophic respiration; NPP = GPP − respiration.

Redfield ratio

The approximate elemental composition of marine organic matter: C:N:P = 106:16:1.

New production

Production supported by nitrogen newly supplied to the euphotic zone from outside the local recycling system, commonly nitrate from deep water.

Recycled production

Production supported by nutrients regenerated within the euphotic zone, especially ammonium.

Compensation depth

The depth where photosynthesis by an individual phytoplankton cell equals its respiration, resulting in zero net production.

Critical depth

The depth where depth-integrated community photosynthesis equals integrated community losses.

Oligotrophic

Describes waters that are nutrient-poor and generally have low biological productivity.

Coriolis effect

The apparent deflection of moving water caused by Earth's rotation; toward the right in the Northern Hemisphere and left in the Southern Hemisphere.

Latent heat flux

Transfer of heat associated with a change in water's physical state, such as evaporation or condensation.

Van der Waals forces

Weak intermolecular attractions between molecules.

Holoplankton

Organisms that remain planktonic for their entire life cycle.

Phytoplankton

Microscopic marine primary producers that use photosynthesis and form the base of most marine food webs.

Diatoms

Phytoplankton with silica-based frustules that often become abundant in nutrient-rich conditions.

Dinoflagellates

Flagellated phytoplankton capable of movement; many thrive in stratified waters, and some cause harmful algal blooms.

Coccolithophores

Phytoplankton covered with calcium-carbonate plates called coccoliths that contribute to marine carbon cycling.

Phytoplankton bloom

A rapid increase in phytoplankton biomass when growth exceeds losses.

Deep chlorophyll maximum

A subsurface depth where chlorophyll concentration is highest; it does not necessarily represent maximum photosynthetic productivity.

Community composition

The identity and relative abundance of different species or groups within a community.

Species richness

The number of different species present in a particular area or community.

Species turnover

The change in which species are present in a community through space or time.

Harmful algal bloom (HAB)

A phytoplankton bloom that negatively affects organisms or ecosystems, often through toxins or oxygen depletion.

Nitrate (NO₃⁻)

An inorganic nitrogen nutrient used by phytoplankton to build proteins and nucleic acids; an important form of new nitrogen.

Ammonium (NH₄⁺)

A form of inorganic nitrogen commonly produced through regeneration and used as a recycled nitrogen source.

Phosphate (PO₄³⁻)

An inorganic phosphorus nutrient required for ATP and nucleic acids.

Silicic acid [Si(OH)₄]

A dissolved form of silicon used by diatoms to build their silica frustules.

Iron (Fe)

A trace nutrient important for photosynthesis and enzyme function.

Nutrient limitation

A condition in which phytoplankton growth is restricted because an essential nutrient is insufficient.

Remineralization

Decomposition of organic matter that converts nutrients back into inorganic forms that can be reused.

Nutrient desert

A region, especially a strongly stratified subtropical gyre, where surface nutrients are very low and productivity is limited by nutrient supply.

Critical Depth Hypothesis

Sverdrup's hypothesis that a bloom can develop when the mixed layer becomes shallower than the critical depth, allowing integrated production to exceed losses.

Critical Turbulence Hypothesis

The idea that bloom development depends on turbulence or mixing strength because weak enough mixing can allow phytoplankton to remain in favorable light even when the mixed layer is deep.

Mixed Layer Eddy Hypothesis

The idea that eddies can create localized shallow stratification that improves light conditions and promotes phytoplankton growth.

Dilution Recoupling Hypothesis

The idea that deepening the mixed layer can dilute phytoplankton and grazers, potentially reducing grazing pressure and allowing phytoplankton biomass to increase.

Community loss

Processes that decrease phytoplankton biomass, including respiration, grazing, sinking, and mortality.

Righetti et al. main finding

Global phytoplankton richness is highest in the tropics, declines toward mid-latitudes, reaches a minimum in temperate regions, and rises slightly toward the poles.

Strongest driver of phytoplankton richness

Sea-surface temperature, which explained about 76% of global variation in diagnosed richness in Righetti et al.

Tropical phytoplankton richness

Phytoplankton richness is highest in the inner tropics, averaging more than 240 species in the study's model.

Temperate richness minimum

Phytoplankton richness reaches a pronounced minimum around approximately 45–65° latitude in both hemispheres.

Physiological tolerance hypothesis

The hypothesis that low diversity occurs because few species have thermal niches that overlap under certain temperature conditions.

Temperature-richness relationship

Richness generally increases with temperature, but at lower temperatures the relationship becomes nonmonotonic, showing that temperature alone cannot explain global phytoplankton diversity.