Marine Ecosystems and Food Webs

Marine Ecosystems and Food Webs

Carbon Cycle

Marine Biota

Export Production

Export Production of Organic Carbon

Trophic levels and dynamics

Ocean Ecosystem Structure







Example of a more complex Food Web


Energy Transfer between Trophic Levels is not efficient



Food Web

Energy

ENERGY

How about Mass Transfer?

How do we measure Biomass?

Mass transfers are more easy to keep track than energy transfers

Alaska

200 km

Large scale Eddies

• Color sensor satellites: MODIS, SeaWiFS, MERIS, OCTS, and CZCS http://oceancolor.gsfc.nasa.gov/SeaWiFS

A simplified diagram of an ecosystem

A useful way to keep track of biomass in the lower trophic levels is to follow the path of MACRONUTRIENTS

Carbon C Nitrogen N

Phosphorus P

Redfield Ratio

C : N : P106 : 16 : 1

Redfield A.C., On the proportions of organic derivations in seawater and their relation to the composition of plankton. In James Johnson Memorial Volume. (ed. R.J. Daniel). University Press of Liverpool, pp. 177-192, 1934. This works stems from his participation as a physiologist in the voyages of WHOI's first research vessel Atlantis.

Atlantis in 1934and today

source 1) atmosphere

source 1) not biological, not atmospheric2) fluvial

C : N : P

source 1) from N2 atmosphere gas2) ocean subsurface3) remineralization of dead organic matter4) biological (e.g. excretions)

At large Nitrogen appears to be the limiting factorin ocean productivity in today’s oceans

What is the explanation for the Redfield ratio?

• Redfield (1958) “biological control of chemical factors" in the ocean: living organisms in the ocean evolved to have a N:P ratios of about 16 → when N is not limiting then N and P but also C and O interact to produce this relation.

• Very stable in deep ocean • Not so stable between phytoplankton species.

• Perhaps only general average?

N

D

P

Z

h

S(No-N) n

NP

k N

DD zZZ

Pg

Pg2

2

Pp

h

Dws

2Zz

2

2(1 )

g PZ

g P

Simple Nitrogen ModelN=nitrogenP=phytoplank.Z=zooplank.D=detritus

~1 Pg C(0.2 % of photosynthetic biomass)

NPP

Net Primary Production (NPP) ~45 Pg C/yr

Phytoplankton biomass turns over in about a week!

NO3

Chlorophyll

Largedetritus

Organic matter

N2 NH4 NO3

Water column

SedimentSediment

Phytoplankton

NH4

Mineralization

Uptake

Nitrification

Nitrification

Grazing

Mortality

Zooplankton

Susp.particles

Aerobic mineralizationAerobic mineralizationDenitrificationDenitrification

N2

Fixation

Mix Layer depth

Description of the oceanic ecosystem based on Nitrogen exchanges

Carbon Cycle

Marine Biota 45 GIC/yr

Export Production

What are the controls on Primary Production?

Ocean Circulation (e.g. gyres, coastal upwelling, eddy fluxes) modulates the fluxes of essential nutrients

Ocean nutrient inventory

Utilization of nutrients in HNLC (High Nutrients Low Chlorophyll regions)

Changes in Redfield Ratio

Export Production of Organic Carbon






Nutrient Sources for Primary Production

The flux of organic carbon must be sustained by an adequate flux of macronutrients

If macronutrients are unavailable then primary production is reduced!


Surface CHL-A

1) Central Gyres 2) Upwelling Regions

Phytoplankton Blooms and Physical Environment

Bands of the dionflagellate Lingulodinium polyedrum moving onshore over the troughs of a series of internal waves

Nonlinear Internal Waves and Phytoplankton

Isopycnals








Nitrogen appears to be the limiting factor for growth in modern time.

C : N : P106 : 16 : 1


N* = N – 16 P (Gruber & Sarmiento 1997)N* = N – 16 P (Gruber & Sarmiento 1997)

N = 25790

NN22 fixation fixation

DenitrificationDenitrification

Modern TIME






Southern Ocean HNLC

Map of annual average nitrate concentrations in the surface waters of the oceans. Data from

Levitus, World Ocean Atlas, 1994.











Climate

Variabilit

y and Change

Marine Ecosystems and Food Webs

Documents

oceanic ecosystem

ocean subsurface

ocean productivity

deep ocean

lower trophic levels

redfield ratiowhat

eddy fluxes

track of biomass