Beschreibung: Time series of hydrographic and transient tracer measurements were used to study the variability of Greenland Sea water mass transformation between 1991 and 2000. Increases in tracer inventories indicate active renewal of Greenland Sea Intermediate Water (GSIW) at a rate of 0.1 to 0.2 Sv (1 Sv = 1 × 106 m3 s−1) (10-year average). A temperature maximum (Tmax) was established at the base of the upper layer (500 m) as a consequence of anomalously strong freshwater input into the near-surface layer at the beginning of the 1990s. Tmax rapidly descended to 1500 m by 1995 followed by a much slower rate of descent. GSIW became warmer and less saline compared to the 1980s. During the deepening phase of Tmax, atmospheric data revealed above-average wind stress curl and oceanic heat loss. In addition, high Arctic Ocean sea-ice export and lack of local sea-ice formation have been documented for that period. A combination of all these factors may have evoked the renewal of GSIW with anomalously freshwater from the upper layers. The Tmax layer established a stability maximum that inhibits vertical exchange between intermediate and deeper waters. Temperature and salinity of deep waters continued to increase at rates of 0.01°C yr−1 and 0.001 yr−1, respectively. However, since 1993, decrease in and homogenization of deep water transient tracer concentrations indicate that renewal occurred predominantly by addition of Arctic Ocean waters. In 2000 the water column (500 m to 3400 m) required an additional 60 W m−2 (110 W m−2) over the annual mean heat loss to restore its heat content to 1989 (1971) values.

Beschreibung: Water column data of carbon and carbon relevant hydrographic and hydrochemical parameters from 188 previously non-publicly available cruises in the Arctic, Atlantic, and Southern Ocean have been retrieved and merged into a new database: CARINA (CARbon IN the Atlantic). The data have been subject to rigorous quality control (QC) in order to ensure highest possible quality and consistency. The data for most of the parameters included were examined in order to quantify systematic biases in the reported values, i.e. secondary quality control. Significant biases have been corrected for in the data products, i.e. the three merged files with measured, calculated and interpolated values for each of the three CARINA regions; the Arctic Mediterranean Seas (AMS), the Atlantic (ATL) and the Southern Ocean (SO). With the adjustments the CARINA database is consistent both internally as well as with GLODAP (Key et al., 2004) and is suitable for accurate assessments of, for example, oceanic carbon inventories and uptake rates and for model validation. The Arctic Mediterranean Seas include the Arctic Ocean and the Nordic Seas, and the quality control was carried out separately in these two areas. This contribution provides an overview of the CARINA data from the Nordic Seas and summarises the findings of the QC of the salinity data. One cruise had salinity data that were of questionable quality, and these have been removed from the data product. An evaluation of the consistency of the quality controlled salinity data suggests that they are consistent to at least ±0.005.

Beschreibung: We present long-term observations of temperature, salinity, tritium/3He, chlorofluorocarbon-11 (CFC 11), and chlorofluorocarbon-12 (CFC 12) for the central Greenland Gyre. The time series span the periods between 1952 and 1994 (temperature), 1981 and 1994 (salinity), 1972 and 1994 (tritium/3He), and 1982 and 1994 (CFCs). The correlation between hydrographic and transient tracer data indicates that low temperatures in the deep water in the early 1950s and between 1960 and 1980 reflect periods of higher deep water formation rates whereas periods of increasing temperatures in the late 1950s and between 1980 and 1994 are related to low deep water formation rates. However, the transient tracer observations obtained in the 1980s and early 1990s indicate that even during periods of low deep water formation, some water from the upper water column contributed to deep water formation between 1980 and 1994. In 1994, the deep water reached temperatures and salinities of −1.149 °C and 34.899, respectively, and no longer fits most of the classical definitions of Greenland Sea Deep Water (−1.29°C〈 Θ 〈 −1.0°C, 34.88〈S〈34.90). The temperature increase in the water column between 200 and 2000 m depth between 1980 and 1994 corresponds to an average heating rate of about 5 Wm−2 over this period, resulting in a decrease in density. The 13-year warming could be balanced by intensive cooling in two winters. The surface salinity steadily increased from 34.50 in 1991 to 34.85 in 1994.

Beschreibung: The transformation rates of upper water into intermediate water (500 to 1600 m) of the central Greenland Sea are deduced from annual changes in CFC tracer inventories between 1991 and 2000. Transformation was found to be intermittent in time, mainly taking place in the winters of 1994/1995 and 1999/2000. Formation rates are of the order of 0.2 to 0.9 Sv (1 Sv = 106 m3 s_1), equivalent to a 10-year average of up to 0.2 Sv. Associated changes in heat content of the intermediate layer are consistent with a winter-time heat loss of 20 W m-2 over 1 month (75 W n r 2 over 1 week) at the sea surface.

Beschreibung: Hydrographic, nutrient and halocarbon tracer data collected in July–August 1994 in the Norwegian Sea, the Faroe Bank Channel (FBC), the Iceland and Irminger Basins and the Iceland Sea are presented. Special attention was given to the overflow waters over the Iceland–Scotland Ridge (ISOW). The Iceland–Scottland overflow water (ISOW) was identified along its pathway in the Iceland Basin, and entrainment of overlying water masses was quantified by multivariate analysis (MVA) using principal component analysis (PCA) and Partial Least Square (PLS) calibration. It was concluded that the deeper portion of the ISOW in the FBC was a mixture of about equal parts of Norwegian Sea Deep Water (NSDW) and Norwegian Sea Arctic Intermediate Water (NSAIW). The mixing development of ISOW during its descent in the Iceland Basin was analysed in three sections across the plume. In the southern section at 61°N, where the ISOW core was observed at Full-size image (〈1 K) depth, the fraction of waters originating north of the ridge was assessed to be 54%. MVA assessed the fractional composition of the ISOW to be 21% NSDW, 22% NSAIW, 18% Northeast Atlantic Water (NEAW), 11% Modified East Icelandic Water, 25% Labrador Sea Water (LSW) and 3% North East Atlantic Deep Water. It may be noted that the fraction of NEAW is of the same volume as the NSDW. On its further path around the Reykjanes Ridge, the ISOW mixed mainly with LSW, and at 63°N in the Irminger Basin, it was warmer and fresher (θ=2.8°C and S=34.92) than at 61°N east of the ridge Full-size image (〈1 K). The most intensive mixing occurred immediately west of the FBC, probably due to high velocity of the overflow plume through the channel, where annual velocity means exceeded Full-size image (〈1 K). This resulted in shear instabilities towards the overlying Atlantic waters and cross-stream velocities exceeding Full-size image (〈1 K) in the bottom boundary layer. The role of NSAIW as a component of ISOW is increasing. Being largely a product of winter convection in the Greenland Sea when no Greenland Sea Deep Water (GSDW) is formed, it spreads above the older and denser deep water in the Nordic Seas. Little or no GSDW, which earlier was considered to be the principal overflow water, has been formed since 1970. This shows that the Iceland–Scotland overflow may also be maintained with intermediate waters as the principal overflowing component. Decadal variability in ISOW properties has not been insignificant, as since the early 1960s there has been a decrease in salinity and temperature, by 0.06 and up to 0.5°C, respectively. Such a trend applies also to the LSW, particularly in the Irminger Basin, where it was warmer, saltier and less dense in the late 1950s and early 1960s Full-size image (〈1 K) than in 1994 Full-size image (〈1 K). CFC tracers were used to assign apparent ages of water masses, showing that the NSDW had an apparent age of about 30 years and that the age of Iceland Sea Deep Water exceeded 25 years. NSAIW observed in the southern Norwegian Sea was estimated to be 6–16 years old. An upper age limit of LSW in the Iceland Basin was found to be 18–19 years. It was further concluded that the products of the onset of intense wintertime convection in the Labrador Sea in the late 1980s were not yet observed in the northern central part of the Iceland Basin. The LSW in the Irminger Basin was found to be significantly younger. Two layers were found there. A shallower layer at a depth of 1000–Full-size image (〈1 K) depth was older than the layer beneath by about 4 years, while the deeper layer at 1500–Full-size image (〈1 K) depth was assessed at an apparent age ranging between less than 1 (formed during the previous winter) and 4 years.