global trends, spatial and temporal scales of marine production

• phytoplankton production is controleld by processes acting at many spatial and temporal scales, from micrometers to ocean basins, and from hours to centuries

what is plankton and primary production

• organisms too small to swim against currents

• includes:

  • phytoplankton

  • zooplankton

  • bacterioplankton

• basal production includes algae + bacteria

  • gross primary production (GPP)

    • photosynthesis by algae

  • bacterial production

    • biomass production from organic or inorganic substrates

  • both of these depend on light, nutrients, and temperature

what controls phytoplankton?

• bottom up factors

  • light

  • nutrients

  • trace elements

  • temperature

  • salinity

• top down factors

  • zooplankton grazing

  • parasites

  • viral lysis

  • cell death

• these forces operate at different spatial and temporal scales, leading to high variability

scales in the ocean

• spatial scales

  • vertical: micrometers .> water column

  • horizontal:

    • mesoscale (eddies, fronts)

    • regional (upwelling systems)

    • basin scale (gyres)

• temporal scales

  • hours-days: tides, diel cycles

  • seasonal: blooms

  • interannual: ENSO

  • decadal-centennial: climate change

the role of ocean physics

• the marine environement is hghly dynamic

• key physical drivers

  • wind (atmospheric circulation)

  • earth’s rotation (coriolis effect)

  • water density (temperature + salinity)

  • continents and bathymetry

  • trubulence (chaotic mixing)

• physics controls

  • nutrient cupply

  • ligth exposure

  • stratification vs mixing

vertical scales: teh water column

• euphotic zone: enough light for photosynthesis

• compensation depth: photosynthesis = respiration

• thermocline: temperature gradient layer

• deep chlorophyll maximum (DCM):

  • not necessarily at surface

  • often below surface where nutrients increase but light is still sufficient

• maximum chlorpphyll does not mean maximum production

horizontal scales: ocean provinces and gyres

oceanographic provinces

• 56 ecological provinces

• grouped into:

  • coastal

  • trade wind (tropical)

  • westerly (temperate)

  • polar systems

• each province has characterisitc:

  • circulation

  • nutrients

  • phytoplankton communities

oceanic gyres

• driven by wind + coriolis force

• characterised by:

  • strong western boundary currents (e.g. gulf stream)

  • oligotrophic centers (low nutrients)

• different productivity on eastern vs western sides

upwelling systems

• occur along the west coast of continents

• caused by wind + ekman trasnport

• bring nutrient rich deep water to surface

• often dominated by diatoms

• among the most productive ecosystems on earth

• includes: coastal and equatorial upwelling

downwelling

• surface water pushed downwards

• low surface prodcutivity

mesoscale features (10-100km)

• eddies

• fronts

• turbulence patches

• mesoscale processes can: enhance nutrient supply

• trigger blooms (e.g. coccolithophore blooms)

• create patchiness in plankton distributions

temporal scales of productivity

• daily

  • diel cycles in photosynthesis and cell division

  • unique to marine systems (continuous mixing)

• monthyl

  • spring-neap tide cycles affecting mixing

• seasonal

  • spring blooms (diatoms → dinoflagellates)

  • strong latitudinal differences:

    • tropical: weak seasonality

    • temperate: strong spring bloom

    • arctic: extreme seasonality

• interannual

  • el nino reduces upwelling

  • leads to:

    • low phytoplankton biomass

    • reduced fisheries (e.g. anchovy collapse)

• long term (climate change)

  • oberved changes in long-term time series (e.g. ALOHA station)

  • warming, stratification, acidification alter productivty patterns

sampling the ocean

• historical

  • challenger expedition

• modern approaches

  • eulerian sampling (fixed location)

  • langrangian sampling (following water masses)

• tools

  • CTD rosettes

  • nets

  • drifting bouys

  • gliders

  • satellites (ocean colour → chlorphyll)

• satellite limitations

  • only surface signal

  • cloud cover

  • cannot detect subsurface chlorphyll maxima