Publication Date:
2022-05-25
Description:
Submitted in partial fulfillment of the requirements for the degree of
Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution
April, 1976
Description:
The marine geochemical cycles of iron, copper, nickel, and cadmium were studied in order to provide a basis for
oceanographic models for trace metals.
Copper, nickel, and cadmium can be determined in a 100 ml seawater sample using cobalt pyrrolidine dithioacarbamate chelate coprecipitation and graphite atomizer atomic absorption spectrometry. Concentration ranges likely to be encountered and estimated (1δ) analytical precisions are copper, 1 to 6 nanomole/kg (±0.1); nickel, 3 to 12
nanomole/kg (±0.3); and cadmium, 0. 0 to 1.1 nanomole/kg (±0.1).
The technique may be applied to freshwater samples with
slight modification.
A survey of several east coast U. S. estuaries established
that an iron removal process occurs commonly when rivers mix
with seawater. Laboratory mixing experiments using water
from the Merrimack River (Mass.) and the Mullica River
(New Jersey) demonstrated that rapid iron precipitation
occurs as negatively-charged iron-organic colloids react
with seawater cations and coagulate. This phenomenom was
modeled using a synthetic, organic-stabilized colloidal
suspension of goethite. The generality of the mechanism
suggests that the world-average net river input of iron
to the oceans is less than 1 μmole/kg of river water, an
order of magnitude below previous estimates.
Profiles of cadmium were obtained for 3 GEOSECS stations
in the Pacific Ocean. Cadmium shows a consistent
linear correlation with phosphate which demonstrates that
cadmium is regenerated in a shallow cycle within the water
column. The water column correlation is consistent with data
on cadmium in marine organisms. Cadmium is enriched in upwelling
regions which explains reports of cadmium enrichment in plankton
from the Baja California upwelling region.
Copper and nickel measurements have been made for three
profiles from the Pacific Ocean. Observed copper concentrations
range from 1 to 6 nanomole/kg; nickel varies from 3 to 12
nanomole/kg. Copper and nickel are removed from surface
waters by uptake into organisms. As noted previously, nickel
is regenerated partially in a shallow cycle (like P) and also
in a deep cycle (like Ba). Copper is regenerated from
biological debris at the bottom but is also scavenged from
the mid and deep water column by an undetermined mechanism.
The scavenging residence time is 1400 years. An estimate
for the continental input of Ni, 7 nanomole/kg of river
water, and Cu, 18 nanomole/kg of river water, was derived
from measurements in the Amazon estuary. The oceanic
residence times for nickel and copper are about 10,000 years.
Evidence available on the uptake laws for trace metals
by plankton suggests that a consistent relationship between
the uptake law and the depth of regeneration may apply.
Description:
Money
in support of this research came at various times from
the ONR, MIT UROP office, and a grant from the Doherty
Foundation.
Keywords:
Geochemistry
;
Chemical oceanography
;
Trace elements in water
;
Chain (Ship : 1958-) Cruise CH115
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
4112508 bytes
Format:
application/pdf
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