The open ocean - factors effecting primary productivity: physical (currents and light)

Question 1

Currents - what is the critical value? critical depth?

Answer 1

Critical depth (total gross photosynth. = total respiration) or total O2 produced 
- total O2 consumed - the critical value is when these are equal

Question 2

what is critical depth always deeper than? Why? light and critical depth?

Answer 2

• Always deeper than compensation depth due to vertical mixing (turbulence)
○ Less light as you get deeper = eventually do not get enough light to meet resp. needs = critical depth
○ Light + nutrients interacting w seasonality

Question 3

look at graph of mixing depth

Answer 3

ok

Question 4

winter mixing depth and light

Answer 4

Winter mixing = greater depth, less light input

Question 5

when will a bloom develop?

Answer 5

If P>R, a bloom will develop, when mixing depth is less than critical depth

Question 6

when will a bloom fail

Answer 6

If P

Question 7

describe turbulence in winter. what impacts it? Water mixing, density, mixing depth

Answer 7

• Turbulence is greater in winter
○ Stormy, upwelling, current divergence = H2O mixed
○ Water density equal in column
○ Phytoplankton forced to great depth (no light; no blooms)
○ Mixing depth is deep
○ Don’t get stratified - get mixed
○ Get lots of nutrients bc of upwelling, but do not increase in numbers = no blooms

Question 8

describe turbulence in spring. what impacts it?

Answer 8

• Turbulence in Spring
○ Less storms, solar heating, H2O col. Stability
○ Density differences
○ Lower mixing depth
○ Phytoplankton trapped by thermocline (drastic change in temp, get trapped in layer bc of stratification)
○ Die and sink at compensation depth
○ After bloom, they experience a crash bc they use up the nutrients

Question 9

describe turbulence in fall. what impacts it?

Answer 9

○ In fall, water turnover and phytoplankton increase
○ Get new production: nutrient supply from deeper waters - critical for phytoplankton regrowth
○ Regeneration production: nutrients recycled - through death of plankton - upwelling brings the nutrients from their decomp. Up

Question 10

what does the depth of light penetration depend on?

Answer 10

• Depth of penetration depends on:
○ Absorption/transparency by H2O
○ Wavelength of light
○ Surface reflection/suspended particles reflection
Latitude, season (seasons of rain, really impacts, runoff of sediment into the water= scattered more), environmental (clouds)

Question 11

what happens to light when it hits the ocean? look at graphs

Answer 11

• Light in H2O is scattered and absorbed
  
  • Violet/red absorbed first, then green and blue
  • Use a variety of wavelengths, but blue goes deeper = use for corals

Question 12

when is photosynth rate peaking? look at graph

Answer 12

Photosynthetic rate peaks while respiration rate is constant with depth