The oxygen isotope composition of water masses in the northern North Atlantic

• Published in: Deep Sea Research Part I: Oceanographic Research Papers
• Main Authors: Frew, R.D., Dennis, P.F., Heywood, K.J., Meredith, M.P., Boswell, S.M.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: 2000
• Subjects: Arctic; Greenland; East Greenland; east greenland current; Labrador Sea; North Atlantic; Northeast Atlantic; Northwest Atlantic; Sea ice
• Online Access: http://nora.nerc.ac.uk/id/eprint/108903/; https://doi.org/10.1016/S0967-0637(00)00023-6

The ratio of oxygen-18 to oxygen-16 (expressed as per mille deviations from Vienna Standard Mean Ocean Water, 18O) is reported for seawater samples collected from seven full-depth CTD casts in the northern North Atlantic between 20° and 41°W, 52° and 60°N. Water masses in the study region are distinguished by their 18O composition, as are the processes involved in their formation. The isotopically heaviest surface waters occur in the eastern region where values of 18O and salinity (S) lie on an evaporation–precipitation line with slope of 0.6 in 18O–S space. Surface isotopic values become progressively lighter to the west of the region due to the addition of 18O-depleted precipitation. This appears to be mainly the meteoric water outflow from the Arctic rather than local precipitation. Surface samples near the southwest of the survey area (close to the Charlie Gibbs Fracture Zone) show a deviation in 18O–S space from the precipitation mixing line due to the influence of sea ice meltwater. We speculate that this is the effect of the sea ice meltwater efflux from the Labrador Sea. Subpolar Mode Water (SPMW) is modified en route to the Labrador Sea where it forms Labrador Sea Water (LSW). LSW lies to the right (saline) side of the precipitation mixing line, indicating that there is a positive net sea ice formation from its source waters. We estimate that a sea ice deficit of ≈250 km3 is incorporated annually into LSW. This ice forms further north from the Labrador Sea, but its effect is transferred to the Labrador Sea via, e.g. the East Greenland Current. East Greenland Current waters are relatively fresh due to dilution with a large amount of meteoric water, but also contain waters that have had a significant amount of sea ice formed from them. The Northeast Atlantic Deep Water (NEADW, 18O=0.22‰) and Northwest Atlantic Bottom Waters (NWABW, 18O=0.13‰) are isotopically distinct reflecting different formation and mixing processes. NEADW lies on the North Atlantic precipitation mixing line in 18O–salinity space, ...