Ocean Water Life Ocean Water Life Composition of

Ocean Water & Life

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

PSCI 131: Ocean Water & Life Composition of Seawater

PSCI 131: Ocean Water & Life Composition of Average Seawater

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

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

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

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

PSCI 131: Ocean Water & Life Global Salinity Variation • Salinity varies by latitude

Ocean Acidity • Rising CO 2 in atmosphere impact chemistry of ocean – About 1/3 of human-generated CO 2 ends up dissolved in ocean – p. H drops, seawater becomes more acidic • Impacts on ocean life: – Microbes and corals have trouble building hard parts from Ca. CO 3 because acidic water dissolves Ca. CO 3

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

Temperature and Density • Influence deep-ocean circulation and distribution and types of life • Both vary with depth

Temperature • Surface water temp varies with amount of solar radiation • Low latitudes – High temperature at surface – Rapid decrease in temperature with depth (thermocline) • High latitudes – Cooler surface temperatures – No rapid change in temperature with depth

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

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

PSCI 131: Ocean Water & Life Ocean Water Density • Density is mass per unit volume – How heavy something is for its size • Determines water’s vertical position in ocean • Controlled by temperature and salinity – Higher temp = lower density – Higher salinity = higher density

Variation by latitude • Low-latitudes – Low density at the surface – Density increases rapidly with depth (pycnocline) because of colder water • High-latitudes • High-density (cold) water at the surface • Little change in density with depth

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

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

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

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

Diversity of Ocean Life

Ocean Life • Home to 228, 000 and growing organisms – Bacteria, algae, squid, fish, sharks, whales, etc. • Most life in sunlit surface waters where photosynthesis takes place

Plankton • Floaters – drift with the ocean currents • 2 groups: • Phytoplankton – plants • Zooplankton - animals

Nekton • Swimmers – move independently of ocean currents

Benthos • Bottom dwellers – live on or in ocean bottom

Marine Life Zones • Distribution of marine organisms depends on: – Availability of sunlight – Distance from shore – Water depth

Sunlight Availability • Photic (light) zone – Upper part of ocean – Sunlit – Euphotic zone is near the surface where the light is strong • Aphotic (without light) zone – Deep ocean – No sunlight

Distance from shore • Distance from shore – Intertidal zone—area where land ocean meet and overlap – Neritic zone—seaward from the low tide line, the continental shelf out to the shelf break – Oceanic zone—beyond the continental shelf

Water depth • Pelagic zone—open ocean of any depth • Benthic zone—includes any sea-bottom surface • Abyssal zone—a subdivision of the benthic zone – – – Deep Extremely high water pressure Low temperatures No sunlight Sparse life Food sources include decaying particles from above, large fragments falling, and hydrothermal vents

PSCI 131: Ocean Water & Life Oceanic Productivity

PSCI 131: Ocean Water & Life Controls on Marine Productivity • Primary productivity: rate at which organisms store energy through formation of organic matter using energy derived from • Photosynthesis (solar radiation) • Chemosynthesis (chemical reactions) • What determines how much biomass a given place at a given time can support? • Availability of sunlight • Amount of nutrients in the water

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

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

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

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

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.

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

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

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

PSCI 131: Ocean Water & Life Marine Productivity: Temperate latitudes • Productivity varies by season • Sunlight availability and presence of thermocline change significantly • Winter – low productivity • Spring – limited productivity • Summer – Strong thermocline, no replenishment from below • Fall – Thermocline breaks down, nutrients return to surface

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