Ocean Water & Life

Ocean Water & Life Composition of Seawater Ocean Temperature & Density Variation Oceanic Biological Productivity

Composition of Seawater PSCI 131: Ocean Water & Life Composition of Seawater

Composition of Average Seawater PSCI 131: Ocean Water & Life Composition of Average Seawater

Composition of Normal Seawater PSCI 131: Ocean Water & Life Composition of Normal Seawater Salt sources Minerals from the continents Undersea volcanism

Processes Affecting Salinity PSCI 131: Ocean Water & Life Processes Affecting Salinity Total mass of salt in open oceans doesn’t change, but salinity does Salinity is mass of salt / mass of water So, water must be added/removed for salinity to change

Processes Affecting Salinity PSCI 131: Ocean Water & Life Processes Affecting Salinity Salinity increases if water is removed Evaporation Sea ice formation

Processes Affecting Salinity PSCI 131: Ocean Water & Life Processes Affecting Salinity Salinity decreases if water is added Precipitation Runoff (rivers) Sea ice melting Icebergs melting

Global Salinity Variation PSCI 131: Ocean Water & Life Global Salinity Variation Salinity vs latitude Patterns correspond to air pressure belts

Ocean Temperature and Density Variations PSCI 131: Ocean Water & Life Ocean Temperature and Density Variations

Temperature vs Depth Warm latitudes Cold latitudes PSCI 131: Ocean Water & Life Temperature vs Depth Warm latitudes Cold latitudes

Thermocline Rapid decrease in water temperature with increasing depth PSCI 131: Ocean Water & Life Thermocline Rapid decrease in water temperature with increasing depth Exists year-round in tropics/subtropics Never appears in subpolar/polar latitudes Seasonal in temperate latitudes

Ocean Water Density Controlled by temperature and salinity PSCI 131: Ocean Water & Life Ocean Water Density Controlled by temperature and salinity Higher temp = lower density Higher salinity = higher density

Density vs Depth Warm latitudes Cold latitudes PSCI 131: Ocean Water & Life Density vs Depth Warm latitudes Cold latitudes

Pycnocline Rapid increase in water density with increasing depth PSCI 131: Ocean Water & Life Pycnocline Rapid increase in water density with increasing depth Mirror image of thermocline Temperature has stronger influence on density than salinity

Ocean Water Layering In regions where a thermocline is present PSCI 131: Ocean Water & Life Ocean Water Layering In regions where a thermocline is present Surface mixed zone: warm, well-circulated Transition zone: location of thermocline Deep zone: cold, dark

Ocean Water Layering If no thermocline, then no layering PSCI 131: Ocean Water & Life Ocean Water Layering If no thermocline, then no layering Polar, subpolar, temperate (in winter)

PSCI 131: Ocean Water & Life Oceanic Productivity

Controls on Marine Productivity PSCI 131: Ocean Water & Life Controls on Marine Productivity Total biomass varies spatially (from place to place) and temporally (over time) What determines how much biomass a given place at a given time can support? Availability of sunlight Amount of nutrients in the water

Controls on Sunlight Availability PSCI 131: Ocean Water & Life Controls on Sunlight Availability Sunlight availability in the ocean depends on sun angle Sun angle controlled by Latitude Season Relationship of latitude to sun angle. Relationship of season to sun angle.

Nutrients: What are they? PSCI 131: Ocean Water & Life Nutrients: What are they? Nutrients are elements and compounds dissolved in ocean water (sodium, phosphorous, carbonate, etc.) Needed by phytoplankton to live Phytoplankton live in surface waters These waters become depleted in nutrients as phytoplankton use them up

Nutrients: How are they replenished? PSCI 131: Ocean Water & Life Nutrients: How are they replenished? Upwelling: movement of deeper, colder, nutrient-rich water up to surface If upwelling is limited or prevented, surface waters will have low biomass

Role of the Thermocline PSCI 131: Ocean Water & Life Role of the Thermocline Thermocline restricts vertical water movement Regions with strong thermocline have nutrient-poor surface water Warm latitudes Cold latitudes

Role of Phytoplankton in Productivity PSCI 131: Ocean Water & Life Role of Phytoplankton in Productivity Phytoplankton are the foundation of the marine food web If phytoplankton biomass changes, total biomass changes Diatom and zooplankton biomass in the Barents Sea over 12 months. Diatoms are a type of phytoplankton.

Annual Marine Productivity by Latitude PSCI 131: Ocean Water & Life Annual Marine Productivity by Latitude

Marine Productivity: Polar/Subpolar PSCI 131: Ocean Water & Life Marine Productivity: Polar/Subpolar Low productivity except for mid-summer Surface waters are nutrient-rich Isothermal (no thermocline) year-round But, sunlight is scarce for most of the year In mid-summer, enough sunlight becomes available to cause spike in phytoplankton biomass

Marine Productivity: Tropical/subtropical PSCI 131: Ocean Water & Life Marine Productivity: Tropical/subtropical Low productivity year-round Sunlight is plentiful year-round But, strong thermocline exists year-round Surface waters are well-lit, but nutrient-poor

Marine Productivity: Temperate latitudes PSCI 131: Ocean Water & Life Marine Productivity: Temperate latitudes Productivity varies by season Sunlight availability and presence of thermocline change significantly

Marine Productivity: Temperate latitudes PSCI 131: Ocean Water & Life Marine Productivity: Temperate latitudes Productivity in the temperate-latitude surface ocean over 12 months.

PSCI 131: Ocean Water & Life End of Chapter