Knowledge of the surface heat transfer in coastal inlets would permit studies of their thermal structure and circulation. An assessment is made of data available for calculating the surface heat transfer for the coastal regions of British Columbia and S.E. Alaska. Monthly means of meteorological and oceanographic observations for the years 1961 and 1963 are critically examined for their representativness of conditions that exist over the open water. The location of the observation point is found to be important in choosing values for dew point and wind speed. Formulae for calculating surface heat transfer are examined for their potential applicability to a coastal climate. The calculated net annual surface heat transfer is found to be highest in the southern regions, approximately 90 langleys/day in the Strait of Georgia, and to decrease for more northerly regions, to an approximate balance with no net input in northern Chatham Strait. The annual cycle is found to be strongly modified by fine structure, the radiation balance dominating in summer, the convective losses in winter. Comparison of the calculated surface heat transfer with heat storage indicates that the calculations may be accurate to within 20% of the peak values. The range and shape of the surface temperature cycle was found to reflect the influence of advection, and deep water temperature, as well as the surface heat transfer. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

No description available.

Thesis (M.Sc.)--Memorial University of Newfoundland, 1994. / Typescript. Bibliography: leaves 74-76. Also available online.

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The representation of deep convection in ocean models is a fundamental challenge for climate science. Here a regional simulation of the Labrador Sea circulation and convective activity obtained with the Regional Oceanic Modeling System (ROMS) over the period 1980-2009 is used to characterize the response of convection to atmospheric forcing and the variability in its seasonal cycle. This integration compares well with the sparse in time and space hydrographic surveys and ARGO data (Luo et al. 2012). It is found that convection in the convective region of the Labrador Sea has experienced variability in three key aspects over the 30 years considered. First, the magnitude of convection varies greatly at decadal scales. This aspect is supported by the in-situ observations. Second, the initiation and peak of convection (i.e. initiation and maximum) shift by two to three weeks between strong and weak convective years. Third, the duration of convection varies by approximately one month between strong and weak years. The last two changes are associated to the variability of winter and spring time heat fluxes in the Labrador Sea, while the first results from changes in both atmospheric heat fluxes and oceanic conditions through the inflow of warm Irminger Water from the boundary current system to the basin interior. Changes in heat fluxes over the Labrador Sea convective region are strongly linked to large scale modes of variability, the North Atlantic Oscillation and Arctic Oscillation. Correlations between the mode indices and the local heat fluxes in the convective area are largest in winter during strong, deep events and in spring whenever convection is shallow.

Storm-induced open-ocean convective mixing is one of the primary processes controlling the supply of nitrate to the sunlit layer of the oligotrophic North Atlantic Subtropical Gyre (NASG). Yet, the magnitude and timing of nitrate fluxes during winter convection is poorly understood due to an absence of targeted process studies. In the northwest NASG, multiple quasi-Lagrangian studies were conducted during the boreal winters of 2004 and 2005 in an effort to sample strong winter convection. During each of the time-series studies, inventories of vertically fluxed nitrate were quantified approximately every twelve hours using the distribution of helium isotopes ([delta]�He) and nitrate in the water column. This method is known as the Helium Flux Gauge Technique (HFGT). Large variability in surface forcing and density structure of the upper ocean was observed between the two years; however, only winter 2005 experienced convective mixing to depths greater than 150 m. In winter 2004, mild atmospheric conditions coincided with a positive phase in the winter North Atlantic Oscillation (NAO), consistent with the dominant regime experienced during the previous decade. On average 36 � 9 mmol m[-2] of fluxed nitrate was inferred by excess �He in the mixed layer of the ocean during the winter 2004 study period. This inventory of physically transported nitrate is attributed to the sampling of waters laterally advected from nearby eddy features. The sampling of multiple water masses is likely due to the inability of the drogue to persistently follow water masses efficiently. Although physical evidence indicates spatial variability within the time-series data, the length scales of convective mixing appear to be greater than those associated with spatial aliasing as a result of drogue performance. This observation provides us with increased confidence that the objectives for the present study are not compromised by spatial variability in the data. In contrast, winter 2005 experienced a negative NAO, strong physical forcing and convective mixing to depths > 250 m. Two convectively modified water masses, most likely resulting from a single storm event, were sampled at different stages of development. These two water masses exhibit large variability in the magnitude of nitrate entrained in the convective layer from the thermocline. An average inventory of 247 � 56 mmol NO₃[-]m[-2] was entrained in the rapidly expanding convective layer of the first water mass in the first few days following the storm approach. In contrast, ongoing entrainment of nitrate was absent from the second water mass, sampled two weeks later when the depth of the surface mixed layer was consistently ~ 300 m. These results indicate that surrounding fluid is entrained into the convective layer when it is actively expanding in the vertical. On the other hand, significant fluid entrainment does not occur at the base of the plume once sinking waters have reached a level of neutral buoyancy. The persistence of elevated nitrate stocks (~ 100 mmol m[-2]) in the convective layer two to three weeks after the inferred injection event, suggests sub-optimal nitrate uptake by resident phytoplankton. Phytoplankton growth was most likely resource limited by light or a micronutrient such as iron. Despite the implied biolimitation, changes in chlorophyll-a, a proxy for phytoplankton biomass, indicate net production within the convective layer. On average, the convective layer was observed to support an inventory of 62 � 6mg chlorophyll-a m[-2], increasing at an average rate of 3.4mg m[-2] d[-1]. This inventory indicates a slow build-up of phytoplankton biomass to near bloom levels, ahead of the main spring bloom that typically follows formation of the seasonal thermocline near Bermuda. Net production in the convective layer was likely due to transient periods of increased (weak) surface stability that were observed to support high phytoplankton biomass, following the cessation of thermocline fluid entrainment. When nitrate and excess �He in samples collected from the thermocline were regressed for the purpose of quantifying nitrate fluxes, the results showed that between 1.6 - 2.0 [mu]mol kg[-1] of dissolved nitrate was present during formation of the water mass. This suggests the source of this excess (above Redfield ratios) nitrate in the thermocline of the NASG is not local, and has ramifications for local nitrogen fixation budgets determined using geochemical approaches. Thesis supervisors: William J. Jenkins, Senior Scientist, WHOI (United States of America); Philip W. Boyd, Senior Scientist, NIWA (New Zealand); Michael W. Lomas, Senior Scientist, BIOS (Bermuda)

Storm-induced open-ocean convective mixing is one of the primary processes controlling the supply of nitrate to the sunlit layer of the oligotrophic North Atlantic Subtropical Gyre (NASG). Yet, the magnitude and timing of nitrate fluxes during winter convection is poorly understood due to an absence of targeted process studies. In the northwest NASG, multiple quasi-Lagrangian studies were conducted during the boreal winters of 2004 and 2005 in an effort to sample strong winter convection. During each of the time-series studies, inventories of vertically fluxed nitrate were quantified approximately every twelve hours using the distribution of helium isotopes ([delta]�He) and nitrate in the water column. This method is known as the Helium Flux Gauge Technique (HFGT). Large variability in surface forcing and density structure of the upper ocean was observed between the two years; however, only winter 2005 experienced convective mixing to depths greater than 150 m. In winter 2004, mild atmospheric conditions coincided with a positive phase in the winter North Atlantic Oscillation (NAO), consistent with the dominant regime experienced during the previous decade. On average 36 � 9 mmol m[-2] of fluxed nitrate was inferred by excess �He in the mixed layer of the ocean during the winter 2004 study period. This inventory of physically transported nitrate is attributed to the sampling of waters laterally advected from nearby eddy features. The sampling of multiple water masses is likely due to the inability of the drogue to persistently follow water masses efficiently. Although physical evidence indicates spatial variability within the time-series data, the length scales of convective mixing appear to be greater than those associated with spatial aliasing as a result of drogue performance. This observation provides us with increased confidence that the objectives for the present study are not compromised by spatial variability in the data. In contrast, winter 2005 experienced a negative NAO, strong physical forcing and convective mixing to depths > 250 m. Two convectively modified water masses, most likely resulting from a single storm event, were sampled at different stages of development. These two water masses exhibit large variability in the magnitude of nitrate entrained in the convective layer from the thermocline. An average inventory of 247 � 56 mmol NO₃[-]m[-2] was entrained in the rapidly expanding convective layer of the first water mass in the first few days following the storm approach. In contrast, ongoing entrainment of nitrate was absent from the second water mass, sampled two weeks later when the depth of the surface mixed layer was consistently ~ 300 m. These results indicate that surrounding fluid is entrained into the convective layer when it is actively expanding in the vertical. On the other hand, significant fluid entrainment does not occur at the base of the plume once sinking waters have reached a level of neutral buoyancy. The persistence of elevated nitrate stocks (~ 100 mmol m[-2]) in the convective layer two to three weeks after the inferred injection event, suggests sub-optimal nitrate uptake by resident phytoplankton. Phytoplankton growth was most likely resource limited by light or a micronutrient such as iron. Despite the implied biolimitation, changes in chlorophyll-a, a proxy for phytoplankton biomass, indicate net production within the convective layer. On average, the convective layer was observed to support an inventory of 62 � 6mg chlorophyll-a m[-2], increasing at an average rate of 3.4mg m[-2] d[-1]. This inventory indicates a slow build-up of phytoplankton biomass to near bloom levels, ahead of the main spring bloom that typically follows formation of the seasonal thermocline near Bermuda. Net production in the convective layer was likely due to transient periods of increased (weak) surface stability that were observed to support high phytoplankton biomass, following the cessation of thermocline fluid entrainment. When nitrate and excess �He in samples collected from the thermocline were regressed for the purpose of quantifying nitrate fluxes, the results showed that between 1.6 - 2.0 [mu]mol kg[-1] of dissolved nitrate was present during formation of the water mass. This suggests the source of this excess (above Redfield ratios) nitrate in the thermocline of the NASG is not local, and has ramifications for local nitrogen fixation budgets determined using geochemical approaches. Thesis supervisors: William J. Jenkins, Senior Scientist, WHOI (United States of America); Philip W. Boyd, Senior Scientist, NIWA (New Zealand); Michael W. Lomas, Senior Scientist, BIOS (Bermuda)

Large-scale circulation in the northern North Atlantic plays a crucial role in the global climate by influencing ocean storage of atmospheric heat and carbon. Temperature and salinity changes in this region can have important consequences on ocean circulation due to density stratification at sites of deep water formation. Such influences can involve feedback mechanisms related to the Atlantic Meridional Overturning Circulation, which has been shown to influence the hydrography of the northern North Atlantic on decadal timescales. Current expectations are that through increasing sea-ice melting, river discharge, an intensifying hydrological cycle and glacial melt anomalies, future climate change could disrupt North Atlantic circulation patterns with cascading effects on carbon cycling and global climate. These interactions were investigated through circulation changes associated with salinity and freshwater variability, as well as variability in temperature and heat content. Recent changes in phytoplankton concentration and biological productivity in the Labrador Sea were also examined as part of this study. Spatial and temporal patterns of salinity in the North Atlantic were examined with the help of objective analysis and reanalysis salinity products using Argo observations of the recent decade (2005 to 2015). An overall freshening trend was evident, but with clear regional differences, particularly between the western subpolar gyre and the central North Atlantic. In general, the western subpolar region exhibited high interannual variability in surface salinity compared to the central North Atlantic. The western subpolar region also revealed a seasonal pattern of salinity fluctuation related to sea ice retreat and accretion, but with some years (i.e., 2008, 2012 and 2015) showing unusually large and negative salinity anomalies which were not present in the central or eastern North Atlantic. To understand the dominant factors influencing salinity and freshwater in the northern North Atlantic, budgets for liquid freshwater content over the northern North Atlantic were derived using a state-of-the-art ocean state estimate (ECCOv4). Here the subpolar North Atlantic (between $\sim$45\oN and the Greenland Scotland ridge) is distinguished from the Nordic Seas (north of the Greenland Scotland ridge). In a separate investigation ECCOv4 was used to describe global ocean heat budgets at varying spatial and temporal resolutions. This analysis showed that anomalies in temperature tendency are driven by atmospheric forcing at short time scales, while advection is the principle term at long time scales. ECCOv4 budget analysis was then used to investigate mechanisms behind interannual freshwater content variability in the northern North Atlantic over the time period 1992-2015. From the mid-1990s to the mid-2000s warming and salinification occurred in the subpolar North Atlantic. Consistent with the upper layer analysis with Argo-observations, ECCOv4 confirmed an overall freshening since about 2005. This freshening occurs simultaneously with an overall cooling in the subpolar North Atlantic. Advective convergence has been identified as the dominant driver of liquid freshwater content and ocean heat content variability in the subpolar North Atlantic, with liquid freshwater and heat content being anti-correlated. Consistent with the global heat analysis in ECCOv4, our results revealed that forcing is only important for establishing anomalies over shorter time scales (i.e., seasonal to interannual), but advective convergence becomes more important at longer (i.e., decadal) scales. Advection is the dominant term due to changes across the southern boundary on the decadal time scale, while exchanges with the Arctic Ocean have minor impact. Changes in freshwater and heat content in the subpolar North Atlantic due to advection occur through anomalies in the circulation itself, and not by the advection of anomalies in either liquid freshwater or heat content. In contrast to the subpolar North Atlantic, in the Nordic Seas interannual changes in liquid freshwater content are predominantly driven by forcing due to sea ice melting, which is in turn strongly correlated with Arctic sea ice export through Fram Strait. The overall concurrent warming and salinification followed by cooling and freshening in the subpolar North Atlantic suggests a relationship with changes in northward heat and salt transport through the Atlantic Meridional Overturning Circulation. This is consistent with decadal variability in deep convection in the Labrador Sea. It is evident that another consequence of changes in the Labrador Sea deep convection is the potential effects on nutrient availability and thus biological productivity. The Labrador Sea has become more productive in recent years, with mean chlorophyll-a concentrations closely correlated with silicate concentrations in the upper waters, which in turn are strongly correlated with wintertime convection depth. Thus annual production in the Labrador Sea appears to be influenced by the extent of deep winter mixing, thereby linking the Atlantic Meridional Overturning Circulation and deep convection to nutrient availability and ocean productivity in the subpolar North Atlantic.

Thesis (S.M.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 1998. / Includes bibliographical references (leaves 155-161). / A detailed examination of the development of a deep convection event observed in the Greenland Sea in 1988-89 is carried out through a combination of modeling, scale estimates, and data analysis. We develop a prognostic one-dimensional mixed layer model which is coupled to a thermodynamic ice model. Our model contains a representation of the lowest order boundary layer dynamics and adjustable coupling strengths between the mixed layer, ice, and atmosphere. We find that the model evolution is not very sensitive to the strength of the coupling between the ice and the mixed layer sufficiently far away from the limits of zero and infinite coupling; we interpret this result in physical terms. Further, we derive an analytical expression which provides a scale estimate of the rate of salinification of the mixed layer during the ice-covered preconditioning period as a function of the rate of ice advection. We also derive an estimate for the rate of the mixed layer deepening which includes ice effects. Based on these scale estimates and model simulations, we confirm that brine rejection and advection of ice out of the convection area were essential ingredients during the preconditioning process. We also demonstrate that an observed rise in the air temperature starting in late December 1988 followed by a period of moderately cold ~ -10*C temperatures was key to the development of the observed convection event. Finally, we show that haline driven deep convection underneath an ice cover is possible, but unlikely to occur in the Greenland Sea. On the basis of these results, we develop a coherent picture of the evolution of the convection process which is more detailed than that presented in any previous work. We also comment on the likelihood that deep convection occurred in the Greenland Sea in the past two decades from an examination of historical data, and relate these findings to what is known about the inter-annual variability of convective activity in the Greenland Sea / by Vikas Bhushan. / S.M.

In order to explain the observed time-dependent salinity variations in seafloor hydrothermal vent fluids, quasi-numerical and fully numerical fluid flow models of the NaCl-H2O system are constructed. For the quasi-numerical model, a simplified treatment of phase separation of seawater near an igneous dike is employed to obtain rough estimates of the thickness and duration of the two-phase zone, the amount of brine formed, and its distribution in the subsurface. For the fully numerical model, the equations governing fluid flow, the thermodynamic relations between various quantities employed, and the coupling of these elements together in a time marching scheme is discussed. The fully numerical model is benchmarked against previously published heat pipe and Elder problem simulation results, and is shown to be largely in agreement with those results. A number of simulation results are presented in the context of two-phase flow and phase separation within the framework of the single pass model. It is found that a quasi-stable two-phase (liquid + vapor) zone at depth below the hydrothermal discharge outlet gives rise to vent fluid with lower than normal seawater salinity. Additionally, it is shown that increasing the spatial extent of the two-phase zone can lower vent fluid salinity. The numerical approach used in this thesis is able to generate salinity patterns predicted by a widely held conceptual model of vent fluid salinity variation, and may be able to explain the vent fluid salinities and temperatures found at the Main Endeavour Vent Field on the Juan de Fuca Ridge, as this approach is able to produce simulated vent fluid salinities that match observed values from the Endeavour Field vents Dante and Hulk.