Radium isotopes in the Orinoco estuary and Eastern Caribbean Sea

Journal Article · Mon Feb 15 00:00:00 EST 1993 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/92JC02760· OSTI ID:6708491

Moore, W S; Todd, J F ^[1]

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1. Univ. of South Carolina, Columbia (United States)

Radium isotopes provide a means of identifying the source of freshened waters in the ocean and determining the time elapsed since these waters were in the estuary. The authors present evidence that during April, waters from the Amazon mixing zone pass within 50 km of the mouth of the Orinoco River. These Amazon waters are characterized by a lower [sup 228]Ra/[sup 226]Ra activity ratio (AR) than are waters from the Orinoco at similar salinities. During autumn, the increased discharge of the Orinoco displaces the freshened Amazon waters seaward, yet the two can be distinguished clearly. Within the Caribbean Sea, waters of Orinoco origin carry a characteristic radium signature including excess activities of [sup 224]Ra. This isotope may be used to estimate the time elapsed since the waters were removed from contact with sediments. Current speeds based on [sup 224]Ra dating ranged from 15 to 33 cm/s during April. The radium isotopes also provide an assessment of sediment mixing in the estuary. During low discharge (April), considerable mixing of older sediment by physical or biological processes or dredging maintained high activities of [sup 228]Ra in the estuary and produced the highest [sup 228]Ra/[sup 226]Ra AR's yet measured in any estuary. During high discharge (September), a large fraction of the [sup 228]Ra was derived from desorption from fresh sediment rather than mixing of older sediments. Activities of [sup 224]Ra were high in the estuary during both high and low discharge, indicating that considerable mixing of recently introduced sediment must occur during each period. During April, [sup 224]Ra and [sup 228]Ra activities in the water were about equal, indicating that most of the sediment being resuspended had been stored in the estuary long enough to reestablish radioactive equilibrium in the [sup 232]Th decay series (i.e., 20 years). 19 refs., 11 figs., 3 tabs.

• OSTI ID: 6708491
• Journal Information: Journal of Geophysical Research; (United States), Vol. 98:C2; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
58 GEOSCIENCES
RADIUM ISOTOPES
TRACER TECHNIQUES
RIVERS
MIXING
SEAS
CARIBBEAN SEA
DECAY
DESORPTION
DREDGING
EQUILIBRIUM
ORIGIN
RADIUM
RADIUM 224
RADIUM 226
RADIUM 228
SEDIMENTS
WATER
ALKALINE EARTH ISOTOPES
ALKALINE EARTH METALS
ALPHA DECAY RADIOISOTOPES
ATLANTIC OCEAN
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CARBON 14 DECAY RADIOISOTOPES
DAYS LIVING RADIOISOTOPES
ELEMENTS
EVEN-EVEN NUCLEI
HEAVY ION DECAY RADIOISOTOPES
HEAVY NUCLEI
HYDROGEN COMPOUNDS
INTERNAL CONVERSION RADIOISOTOPES
ISOTOPE APPLICATIONS
ISOTOPES
METALS
NUCLEI
OXYGEN COMPOUNDS
RADIOISOTOPES
SORPTION
STREAMS
SURFACE WATERS
YEARS LIVING RADIOISOTOPES
540310* - Environment
Aquatic- Basic Studies- (1990-)
540311 - Environment
Aquatic- Basic Studies- Radiometric Techniques- (1990-)
580000 - Geosciences