? Flashcards

1
Q

what are fronts and what do they come from

A

narrow, high gradient regions - cause upwellings
- when 2 different currents meet: converge or diverge

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1
Q

what are shelf break front

A

edge of continental shelf as a result in change of depth (e.g. coastal waters to very deep waters)

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2
Q

what are estuarine-plume fronts

A

formed by salinity gradient

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3
Q

what’s a tidal mixing front

A

friction between tidal flows and sea bed - create turbulent bottom boundary layer (BBL) - injects nutrients into water column + affects phyto growth
in deeper waters (outer shelf):
- winter: SML overlaps BBL (big SML due to wind)
- spring: SML + BBL = separate
in shallower waters tidal flows + stirring = stronger - water column remains mixed all year

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4
Q

how do tidal fronts affect phyto growth

A

pinger et al 1975 - investigated phyto distribution off the Ushant, summer
- near shore: well mixed (high nutrients), low chl a (also high suspended solids so low light)
- off shore: stratified (phyto already used the nutrients available), low chl a
- front: high chl a - interface between the two - plenty light + plenty nutrients

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5
Q

what’s the largest circulation feature of the globe

A

N pacific gyre - oligotrophic - low f-ratio (high recycling)

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6
Q

what did Karl et al, 1997 find whilst investigating Nitrogen fixation in the north Pacific

A

over 1st + 3rd years: trichodesmium increased significantly - calculated this was able to provide half N required to sustain PON export
- another way assessed changes in N:P ratios - found a drop in this from the Redfield ratio as phyto became increasingly limited

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7
Q

what’s an important source of ‘new’ nitrogen to oligotrophic waters even though N is recycled

A

N2 fiction by trichodesmium - leads to P (not N) controlling / limiting PP rate in the N pacific gyre

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8
Q

what are equatorial upwellings

A

oceanic upwelling - when wind drives the surface water anticlockwise in the north + clockwise in the south meet together (in the equator) it pulls the water apart, drawing nutrient rich water u from below - leads to higher chl a conc

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9
Q

why do we see low chlorophyll conc in the pacific equatorial upwelling

A

high nutrient low chlorophyl area - iron deficient
- galapogas is in the same place yet there is high chl a conc (surrounded by volcanos that fertilise water with Fe)

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10
Q

3 coastal upwelling examples

A
  • Arabian sea monsoon system
  • El Niño
  • Benguela
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11
Q

what happens in the Arabian sea monsoon upwelling system

A

happens near Indian Ocean - increases effects from land weather
- during inter-monsoon periods, wind directions reverse - pushes warm oligotrophic surface waters onto the land - restrains upwellings

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12
Q

what happens in the El Niño upwelling system

A
  • easterly (trade) winds drives warm surface waters to the west - water level ‘piles up’ on the west (La Niña) - causes upwelling of cold nutrient rich water
  • but wind structures can change - potential energy in this pile can be released and flow back to east (El Niño) - effects weather patterns
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13
Q

what happens in the Benguela upwelling system

A

encountered 3 distinct water masses by age (from temp and NO3-):
- initial maturing upwelled water
- intermediate maturing upwelled water
- age maturing upwelled water

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14
Q

initial maturing upwelled water characteristics

A
  • cold + high NO3-
  • High chl a + PP
  • classical food chain
  • diatoms dominate phyto but still high bacteria
  • high f-ratio
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15
Q

intermediate maturing upwelled water characteristics

A
  • higher temp, lower NO3- (most been taken up / fallen out of surface waters)
  • lower chl a + PP
  • diatoms turn to nano flagellates (utilise smaller concs)
  • highest bacteria biomass
16
Q

age maturing upwelled water characteristics

A
  • higher temp, lower NO3- (most been taken up / fallen out of surface waters)
  • low chl a + PP
  • nano flagellates
  • lowest bacterial biomass - kept in check by nano
  • microbial loop
  • low f-ratio