ALBERT

Description: The suggestion is advanced that the remarkably low static stability of Antarctic surface waters may arise from a feedback loop involving global deep-water temperatures. If deep-water temperatures are too warm, this promotes Antarctic convection, thereby strengthening the inflow of Antarctic Bottom Water into the ocean interior and cooling the deep ocean. If deep waters are too cold, this promotes Antarctic stratification allowing the deep ocean to warm because of the input of North Atlantic Deep Water. A steady-state deep-water temperature is achieved such that the Antarctic surface can barely undergo convection. A two-box model is used to illustrate this feedback loop in its simplest expression and to develop basic concepts, such as the bounds on the operation of this loop. The model illustrates the possible dominating influence of Antarctic upwelling rate and Antarctic freshwater balance on global deep-water temperatures.

Description: The importance of decadal climate variability (DCV) research is being increasingly recognized, including by the World Climate Research Program (WCRP) and the Intergovernmental Panel on Climate Change (IPCC). An improved understanding of DCV is very important because stakeholders and policymakers want to know the likely climate trajectory for the coming decades for applications to water resources, agriculture, energy, and infrastructure development. Responding to this demand, many climate modeling groups in the United States, Europe, Japan, and elsewhere are gearing up to assess the potential for decadal climate predictions. The magnitudes of regional DCV often exceed those associated with the trends resulting from anthropogenic changes. Therefore, differentiating between the two is also very important for planning, implementation, and national and international treaties.

Description: Simple idealized layered models and primitive equation models show that the meridional gradient of the zonally averaged pressure has no direct relation with the meridional flow. This demonstrates a contradiction in an often-used parameterization in zonally averaged models. The failure of this parameterization reflects the inconsistency between the model of Stommel and Arons and the box model of Stommel, as previously pointed out by Straub. A new closure is proposed. The ocean is divided in two dynamically different regimes: a narrow western boundary layer and an interior ocean; zonally averaged quantities over these regions are considered. In the averaged equations three unknowns appear: the interior zonal pressure difference Delta p(i), the zonal pressure difference Delta p(b) of the boundary layer, and the zonal velocity us at the interface between the two regions. Here Delta p(i) is parameterized using a frictionless vorticity balance, Delta p(b), by the difference of the mean pressure in the interior and western boundary, and u(delta) by the mean zonal velocity of the western boundary layer. Zonally resolved models, a layer model, and a primitive equation model validate the new parameterization by comparing with the respective zonally averaged counterparts. It turns out that the zonally averaged models reproduce well the buoyancy distribution and the meridional flow in the zonally resolved model versions with respect to the mean and time changes.

Description: Continuous estimates of the oceanic meridional heat transport in the Atlantic are derived from the Rapid Climate Change–Meridional Overturning Circulation (MOC) and Heatflux Array (RAPID–MOCHA) observing system deployed along 26.5°N, for the period from April 2004 to October 2007. The basinwide meridional heat transport (MHT) is derived by combining temperature transports (relative to a common reference) from 1) the Gulf Stream in the Straits of Florida; 2) the western boundary region offshore of Abaco, Bahamas; 3) the Ekman layer [derived from Quick Scatterometer (QuikSCAT) wind stresses]; and 4) the interior ocean monitored by “endpoint” dynamic height moorings. The interior eddy heat transport arising from spatial covariance of the velocity and temperature fields is estimated independently from repeat hydrographic and expendable bathythermograph (XBT) sections and can also be approximated by the array. The results for the 3.5 yr of data thus far available show a mean MHT of 1.33 ± 0.40 PW for 10-day-averaged estimates, on which time scale a basinwide mass balance can be reasonably assumed. The associated MOC strength and variability is 18.5 ± 4.9 Sv (1 Sv ≡ 106 m3 s−1). The continuous heat transport estimates range from a minimum of 0.2 to a maximum of 2.5 PW, with approximately half of the variance caused by Ekman transport changes and half caused by changes in the geostrophic circulation. The data suggest a seasonal cycle of the MHT with a maximum in summer (July–September) and minimum in late winter (March–April), with an annual range of 0.6 PW. A breakdown of the MHT into “overturning” and “gyre” components shows that the overturning component carries 88% of the total heat transport. The overall uncertainty of the annual mean MHT for the 3.5-yr record is 0.14 PW or about 10% of the mean value.

Description: The water mass structure of the Arctic Ocean is remarkable, for its intermediate (depth range ~150–900 m) layer is filled with warm (temperature 〉0°C) and salty water of Atlantic origin (usually called the Atlantic Water, AW). This water is carried into and through the Arctic Ocean by the pan-Arctic boundary current, which moves cyclonically along the basins’ margins (Fig. 1). This system provides the largest input of water, heat, and salt into the Arctic Ocean; the total quantity of heat is substantial, enough to melt the Arctic sea ice cover several times over. By utilizing an extensive archive of recently collected observational data, this study provides a cohesive picture of recent large-scale changes in the AW layer of the Arctic Ocean. These recent observations show the warm pulse of AW that entered the Arctic Ocean in the early 1990s finally reached the Canada Basin during the 2000s. The second warm pulse that entered the Arctic Ocean in the mid-2000s has moved through the Eurasian Basin and is en route downstream. One of the most intriguing results of these observations is the realization of the possibility of uptake of anomalous AW heat by overlying layers, with possible implications for an already-reduced Arctic ice cover.

Description: Vertical mixing in the bottom boundary layer and pycnocline of the Laptev Sea is evaluated from a rapidly sampled 12-h time series of microstructure temperature, conductivity, and shear observations collected under 100% sea ice during October 2008. The bottom boundary turbulent kinetic energy dissipation was observed to be enhanced (ϵ ∼ 10−4 W m−3) beyond background levels (ϵ ∼ 10−6 W m−3), extending up to 10 m above the seabed when simulated tidal currents were directed on slope. Upward heat fluxes into the halocline-class waters along the Laptev Sea seabed peaked at ∼4–8 W m−2, averaging out to ∼2 W m−2 over the 12-h sampling period. In the Laptev Sea pycnocline, an isolated 2-h episode of intense dissipation (ϵ ∼ 10−3 W m−3) and vertical diffusivities was observed that was not due to a localized wind event. Observations from an acoustic Doppler current meter moored in the central Laptev Sea near the M2 critical latitude are consistent with a previous model in which mixing episodes are driven by an enhancement of the pycnocline shear resulting from the alignment of the rotating pycnocline shear vector with the under-ice stress vector. Upward cross-pycnocline heat fluxes from the Arctic halocline peaked at ∼54 W m−2, resulting in a 12-h average of ∼12 W m−2. These results highlight the intermittent nature of Arctic shelf sea mixing processes and how these processes can impact the transformation of Arctic Ocean water masses. The observations also clearly demonstrate that absence or presence of sea ice profoundly affects the availability of near-inertial kinetic energy to drive vertical mixing on the Arctic shelves.

Description: Long-term temperature and current-meter records from moorings in the northern Canary Basin display strong current events with time scales between one and three months and large vertical scales of several thousand meters. The data are compared to hydrographic surveys in the area that show a meandering subtropical front. The strong current events are found to be related to the passage of the front through the mooring positions. An analysis of composite time series, for selected depths, indicates cases of westward and of eastward propagation of frontal meanders. The frontal pattern is also found in geopotential anomalies inferred from historical XBT data sets, suggesting that the front is a persistent feature of the density field. In two cases strong current events appear to be related to a Mediterranean Water lens.

Description: Thirty seven juvenile specimens and one adult specimen of the cranchiid squid Mesonychoteuthis hamiltoni were captured by the opening and closing RMT8 net during RRS ‘Discovery’ cruise 100 (1979) in the Southern Ocean. The collection extends the size ränge of juveniles of this species previously described and illustrated. The small specimens resemble small juveniles of Galiteuthis glacialis, which also occur in most hauls, but are separated on the following characters : (a) M. hamiltoni lacks paired tubercles at the nuchal mantle fusion, (b) M. hamiltoni possesses a more capacious and thicker mantle, which is freer at the nuchal fusion and less constricted posterior to the opening; (c) juvenile M. hamiltoni up to a size of 26.5 mm (the largest in the present collection) have very small fins, while in G. glacialis of this size the posterior portion of the mantle has begun to extend into a tail and prominent fins appears; (d) M. hamiltoni has longer tentacles until it reaches a dorsal mantle length of approximately 25 mm. All specimens of M. hamiltoni were captured to the south of the Antarctic Convergence, and most were captured at depths between 20 m and 500 m apparently concentrated in the upper zone of ‘Warm Deep Water’ beneath the surface layer. Four newly hatched specimens were captured at 55°35’S between 20 and 500 m. The adult specimen was captured in a haul which had sampled a depth horizon from 2 000 m to 2 200 m.

Description: Seventeen advanced macrotritopus “larvae” from 7 to 15 mm mantle length were attracted to underwater lights in St. Croix, U.S. Virgin Islands. Their behavior was observed in situ, then seven were captured alive and one female was reared to an adult Octopus defilippi. The characteristic long arms of the planktonic young appear to function in flotation, feeding, crawling and defense. There is evidence that larger macrotritopus may be planktonic by night and benthic by day; thus the transition from a planktonic to benthic life may be controlled to ensure widespread distribution on to a suitable habitat. Morphological examination of 106 specimens from the Atlantic indicate that all macrotritopus “larvae” from this ocean are O. defilippi.

Description: A methodology is presented for obtaining egg masses from captive populations of the ommastrephid squid Illex illecebrosus and for incubating them intact under controlled conditions. Survival of rhynchoteuthion larvae for 9 days after hatching is the best reported to date, though it has not yet been possible to induce feeding. Factors critical to rearing success are discussed, e.g. tank size, stocking density, turbulence, light levels and photoperiod, as well as food type and concentration.

Description: The unique rhynchoteuthions of the ommastrephid squids are the smallest decapodan cephalopod hatchlings and have never been successfully reared. Based on anatomical and behavioural observations a mechanism of suspension feeding is proposed which depends on direct interception and inertial impaction on the mucus coated body surface. Mucus is transferred to the mouth area by ciliary motion and by observed cleaning behaviours. Suspension feeding is suggested to be a supplement to raptorial feeding but may be a critical "bridge" between small yolk reserves and the minimum development required for effective predation. Loss of ciliature through contact with vessel walls may prevent feeding in culture.

Description: Rhynchoteuthion larvae of three species of ommastrephid squids from Hawaiian waters were identified, and aspects of their ecology examined. Important taxonomic characters for field Identification include the number and location of photophores, length of the proboscis (fused tentacles), size at which the proboscis completely divides and the relative sizes of the suckers on the proboscis tip. Other taxonomic characters include sucker structure and chromatophore patterns. Variation among species were found in both temporal and vertical distributions.

Description: While carrying out a systematic revision of the pelagic squid genus Octopoteuthis, the author examined 146 “larval” specimens of the genus from museum sources worldwide. Individuals could not be separated into species but morphometric and meristic characters were examined giving information on ontogenetic development. Specimens ranged in size from 1.3 to 27.0 mm dorsal mantle length (DML) and represented locations in the Atlantic, Pacific and Indian Oceans and also the Mediterranean Sea. Captures were made with a variety of trawls and plankton nets. The deepest record from a closing net was 1 200 m using a MOCNESS system. The largest group examined totalling 105 individuals was collected in the North Atlantic. In the Atlantic the highest larval occurence was found to be in March, April, and June (which may reflect higher sampling pressure in those months) but specimens were obtained in all months except January and December. Low numbers in each of the other oceans prohibited an evaluation of yearly larval distribution.

Description: Larval squid were sampled in three surveys off the eastern Australian coast in January, March and May 1983. Ommastrephid larvae were abundant and occurred at over 90 % of stations. Although Identification to species level has not so far been possible for the majority of specimens, general patterns of distribution with respect to latitude and bottom depth are presented.