Factors Regulating Primary Productivity

Question 1

What are the factors that affect photosynthesis?

Answer 1

Light quantity and quality, nutrient availability, grazing pressure, temperature

Question 2

What is the role of photosynthesis in the oceans?

Answer 2

Fix CO2 into organic matter, organic matter passes from producers to consumers and into deeper waters, Carbon returned to seawater through respiration, bacterial decomposition of organic matter, deposition locks away C in sediments

Question 3

What is phytoplankton biomass?

Answer 3

The standing stock of the group. Total phytoplankton in a given area or volume of water.

Question 4

What is primary productivity?

Answer 4

The rate at which organic matter is produced by primary producers via photosynthesis

Question 5

What is a phytoplankton bloom?

Answer 5

The accumulation of biomass in a particular area, typically from an increase in primary productivity/cell division

Question 6

What are the units of phytoplankton biomass?

Answer 6

(#cells/gC/N/Chla)/(L/m^2/m^3)

Question 7

What are the methods for measuring chlorophyll?

Answer 7

In vivo fluorescence, in vitro fluorescence, remote sensing

Question 8

What is in vivo fluorescence?

Answer 8

Fluorescence measuring using a flow-through fluorometer towed or part of CTD. Emits blue light and measures red light fluoresced by chlorophyll.

Question 9

What is in vitro fluorescence?

Answer 9

Seawater sampled at various depths and filters, then extract chl from filter and measure in a fluorometer.

Question 10

How does remote sensing measure fluorescence?

Answer 10

Converts measures of ocean color into estimates of chl a from depths between 5-25m and allows oceanographers to see global patterns.

Question 11

What are some important ocean color satellites?

Answer 11

Coastal Zone Color Scanner (1978-1986), Sea-viewing Wide Field-of-view sensor (SeaWiFS) (1997-2010), MERIS (2002-2012), MODIS (2000-present)

Question 12

What is gross primary productivity?

Answer 12

The total amount of organic matter produced by phytoplankton per unit time. (Total PP)

Question 13

What is net primary productivity?

Answer 13

The amount of organic matter produced by phytoplankton available to primary consumers per unit time (GPP - respiration)

Question 14

Is PP proportional to biomass?

Answer 14

Sometimes, but biomass can be low due to grazing but PP can still be high

Question 15

What are the methods for measuring primary productivity?

Answer 15

Satellite (months/globally), O2 mass balance (weeks/mixed layer), incubations (days/specific depths), FRRF (minutes/single cells)

Question 16

What are the incubation methods for measuring primary productivity?

Answer 16

Measure the evolution of O2, measure the uptake of CO2 or N or Si using isotope tracers.

Question 17

How does incubation work?

Answer 17

Incubate seawater samples in light and dark bottles and a different light intensities for several hours

Question 18

What is the O2 technique?

Answer 18

Measures O2 given off by photosynthesis and utilized during respiration

Question 19

What happens to solar radiation as it reaches the sea surface?

Answer 19

1/2 absorbed/scattered in the first few meters. UV scattered, IR converted to heat. 1/2 in the visible spectrum and can penetrate the water (PAR)

Question 20

What factors affect the penetration of visible light through the water column?

Answer 20

Wavelength of light (blue=deeper, red=shallower), clarity of water (more particles=more absorption/scattering). Deeper light penetration in deeper waters

Question 21

How can we estimate k (the attenuation coefficient)?

Answer 21

Using a radiometer (measures light intensity directly), secchi disk (depth at which it disappears is called the secchi disk depth)

Question 22

How doe phytoplankton deal with variability in light quality?

Answer 22

Use accessory pigments to harvest additional light energy. Photosynthesis is proportional to light intensity until Pmax, which changes with species and within species.

Question 23

How does primary productivity change with depth?

Answer 23

Too close to the surface, there is little PP because of denaturation of DNA by UV light, max just below the surface, then decreasing in proportion to the exponential decrease in light intensity.

Question 24

What is the critical depth?

Answer 24

The depth above which total production-total respiration in the water column (depth integrated respiration and production). GPP=R or GPP-R=0.

Question 25

What is the critical depth theory?

Answer 25

If the depth of mixing > Dcr : no phytoplankton bloom, but if depth of mixing < Dcr : phytoplankton bloom.

Question 26

What is the compensation depth?

Answer 26

The depth at which the process of respiration and production are equal, the defining point for the base of the euphotic zone (~0.01Io)

Question 27

How does photosynthesis changes with depth?

Answer 27

Photosynthesis is proportional to light intensity until Pmax, which is the max value of photosynthesis.

Question 28

What affects Pmax?

Answer 28

Depends on the species, environmental conditions (i.e. nutrients), water mass, which affect dark reactions of photosynthesis

Question 29

What is ki?

Answer 29

It is the half-saturation constant

Question 30

What do we use Pmax and ki for comparing species?

Answer 30

Helps determine species dominance. Species that peak at lower intensities may have dominance at deeper depths with lower intensities, but at the same intensity if one species has higher rate of photosynthesis then that species will dominate.

Question 31

What affects the initial curve in a P-I curve?

Answer 31

Depends on physiological changes (efficiency of cells to use light), which affect light reactions of photosynthesis

Question 32

What affects the compensation depth?

Answer 32

Transparency of water (turbidity), availability of light (seasons, latitude)

Question 33

What is the difference between the compensation depth and the critical depth?

Answer 33

The compensation depth is the depth at which the processes of production and respiration are equal (only for that depth), whereas the critical depth is the depth where the column integrated processes are equal

Question 34

Which water conditions are favorable for phytoplankton blooms?

Answer 34

Stable water column conditions can be good for phytoplankton blooms (while nutrients are available), if organisms stay in the light area. If mixing causes organisms to go below the critical depth, it can inhibit them from thriving

Question 35

Is the critical depth shallower or deeper than the compensation depth?

Answer 35

Deeper