Item

Abstract

A chemically reactive 10-layer sediment module was coupled to a
geochemical

ocean

general

circulation

model (the Hamburg

Oceanic

Carbon Cycle

Model). The sediment

model

includes

four solid

sediment

components

(CaCOs,

opal, organic

carbon,

and clay), and five pore water substances

(dissolved

inorganic

carbon,

total

alkalinity,

POS4

-, 02, Si(OH)4)

plus

corresponding

species

containing

tsC and t4C instead

of t2C. The processes,

namely,

particle

deposition,

pore
water reactions, pore water diffusion and interaction with the open water column,
vertical sediment

advection, sediment accumulation, and bioturbation, are simulated
through basic parametrizations. For the water column part the Si and C cycles
are coupled

by a formulation

of the "rain ratio" Si:C(CaCO3):C(POC), where
POC is particulate organic carbon, in biogenic

particle export production, with

CaCO3 frustrule production

growing

in parallel to a weakening

of opal production

during progressing

deficiency

of dissolved

silicate in the surface layer. For two
preindustrial velocity fields the model reproduces

major features of observed

water
column and sediment tracer distributions parallel to a correct preindustrial CO2
level close to 280 ppm. The model reacts sensitively to the formulation of the
POC flux parametrization, the rain ratio, as well as the solubility of opal but is
fairly insensitive

to changes

in the bioturbation rate as well as the amount of clay
deposition. A simulation of the sediment distribution by use of a velocity field,
which represents

the ocean at conditions

during the last glacial maximum, yields

realistic glacial-interglacial

changes

for the Atlantic Ocean, while discrepancies
remain for the Indo-Pacific region. A significant

decrease

of the atmospheric

pCO2

could be achieved

through an additional change

of water column inventories

by a

change

in weathering

input of Si and alkalinity.