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5 Exchange Processes and Overall Budgets I. PRINCIPAL RECOMMENDATIONS The Working Group, noting that determination of the budgets of heat, momentum, salt, and other materials is crucial to understanding the role of the Southern Ocean in global oceanic and atmospheric dynamics, and further noting that such determination will require measurements of the exchange processes by direct or indirect means in areas of strong interaction, e.g., frontal zones, makes the following recommendations: 1. We recommend the initiation of planning for a program of mea- surement of exchange processes in the Southern Ocean. Such planning should draw heavily on satellite observations and on the development of measure- ment techniques and understanding of exchange processes generated by other programs, e.g., NORPAX, CUBA, or JASIN, in other oceans. 2. We recommend that the initial elements of a measurement pro- gram include (a) A detailed survey designed to yield the structure (thermal, haline, alkalinity, C02, and nutrient distribution) of the Polar Front and other frontal areas in various positions and at various times; (b) Estimation of fluxes occurring within gyres and near con- tinental margins to assess the interaction of Antarctic Surface Water south of the Antarctic Circumpolar Current with warmer, saltier deep water. 3. We recommend emphasis on the collection of data during the winter, especially below and within the sea-ice fields, noting that other seasonal data are also critical in refinement of budget studies in the con- tinental margin and open ocean, and that hydrographic and meteorological measurements in the regions of glacial ice be made in conjunction with the various existing and proposed ice-shelf projects. 4. We recommend a continuing program for monitoring standard meteorological variables during all survey programs. This monitoring function 37
38 Southern Ocean Dynamics could eventually be performed by untended data stations and remote-sensing systems. II. INTRODUCTION In this chapter, we present a general discussion of exchange processes in the Southern Ocean and regions important to the overall budgets. It is clear that understanding the role of the Southern Ocean in the global long-term atmospheric and oceanic climate will require certain moni- toring of large-scale exchange processes. It is equally clear that the deter- mination of the magnitude and variability of large-scale energy and property exchanges in any region of the world ocean requires a complex, expensive, and long-term effort. In our recommendations, we have noted that careful and continual planning will be required so that an efficient program can be carried out with maximum use of results from other studies of exchange processes in other oceans. We have listed the initial elements of a possible program. The divergent wind drift and intense thermohaline alterations of the surface waters around Antarctica set up a meridional circulation pattern that carries great quantities of heat, salt, and water from the northern abyssal waters into the Southern Ocean. This water upwells and is altered to cold antarctic water masses, which subsequently spread northward. The sea-air exchanges of heat, salt, and momentum and the exchange of properties between water masses in this region are vigorous, and they are only poorly understood. Of special global interest is the exchange of material across the sea-air interface, which couples the ocean with the atmosphere. The Ant- arctic is of particular significance because, through these waters, the abyssal waters of the world can interact directly with the atmosphere. Based on current understanding of antarctic oceanography, we can outline the procedures that are needed for better definition of the budgets or balances of heat, salt, and mass. Areas of interaction between definable bodies of water whose boundaries are marked by relatively large gradients of temperature and/or salinity are fundamental; primary among these are the frontal zones, continental margins, the main pycnocline, and the large cyclonic gyres. Special attention must be placed on the thermohaline activity below melting, stable, and growing sea-ice covers and within the ice-free areas; the antarctic pack-ice field is characterized by both phenomena. The interac- tion of glacial ice with seawater is clearly of local importance and could be of large-scale importance. The key to all the budget studies is better deter- mination of all the fluxes of heat, salt, and momentum and of the influence of various environmental parameters on these fluxes. Such determination is crucial to the understanding of the role of the Southern Ocean in global oceanic and atmospheric dynamics.
Exchange Processes and Overall Budgets 39 Therefore, we recommend the initiation of planning for a program of measurement of exchange processes in the Southern Ocean. The Working Group notes that it is not feasible at this time to mount a special and large measurement program for this purpose. Extensive efforts are being made in other programs (e.g., NORPAX, JASIN, or CUBA) to determine reliable and accurate techniques for the monitoring of energy and property exchange. Additionally, satellite data from the region have not yet been fully utilized for such studies. To conserve resources, we recommend that planning for a program of measurement of exchange processes in the Southern Ocean draw heavily on satellite observations and on the develop- ment of measurement techniques and understanding generated by other pro- grams in other oceans. In this way, studies in the Southern Ocean can proceed concurrently with studies in other oceans without a requirement for special development. The initial elements of a measurement program must be descriptive: the determination of the magnitude and variability of heat, salt, momentum, and other exchanges. Later elements will include use of the data to elucidate the actual transfer mechanisms accomplishing the fluxes. III. BRIEF OVERVIEW A. MERIDIONAL CIRCULATION AND AIR-SEA INTERACTION The thermohaline interaction of the sea with ice and the atmosphere, coupled with the relatively low stability of the surface water, produces deep- reaching convection in a number of zones in the Southern Ocean. Major regions of sinking occur at the continental margins and frontal zones in the deep ocean. The deepest convection occurs in the production of Antarctic Bottom Water (AABW); at the Polar Front Zone, convection extends to about 1 km in production of Antarctic Intermediate Water (AAIW). Figure 5.1 shows a schematic representation of water mass interaction in the South- ern Ocean [Gordon, 197Ic]. The southward-migrating and upwelling Circumpolar Deep Water (CDW) tends to compensate for the sinking northward-migrating antarctic water mass. The CDW carries toward the sea surface the heat and salt needed to balance sea-air exchange, and it recycles nutrients to maintain the ant- arctic surface water as a fertile area for plankton blooms. The antarctic convection pattern extends by lateral migration below the main thermocline of the world ocean. The northward flow of AABW occurs mainly in deep western boundary flows, and the AAIW represents a layer separating the thermocline waters from the abyssal waters. The AAIW migrates slowly northward in a nearly sheetlike pattern into the South Pacific and Atlantic [Mosby, 1934].
40 Southern Ocean Dynamics SUBAHTAHCTIC -k â¢>«.' ^âANTARCTIC SURFACE . -X«: SURFACE FIGURE 5.1 Water mass distribution on a north-south plane with inferred flow pattern. [A. Gordon, AAAS Pub. No. 93, p. 612. Copyright 1971 by the American Association for the Advancement of Science.] The water composing the two antarctic water masses eventually flows back to the south in each ocean, with important additions of relatively salty but warmer water from the North Atlantic Ocean. The North Atlantic Deep Water (NADW) warms the abyssal waters, since it is warmer than the average abyssal water temperature. This flow of NADW, lower in oxygen but higher in nutrients as a result of oxidation of organic material below the ther- mocline, is incorporated into the CDW and eventually upwells to begin the process again. The NADW is of special importance in adding salt and heat to abyssal water and to the Southern Ocean. The overturning of abyssal waters in the Southern Ocean thus main- tains the abyssal layer as an oxygen-rich, cold environment and provides a "breathing" or recycling mechanism for the abyssal waters. B. APPROXIMATE BUDGETS Unambiguous direct measurement of the transfers of ocean properties due to meridional circulation is not now possible, because the flux per unit area is too small. For example, the approximate magnitude of the meridional volume flux of deep water, 50 x 106 m3/s, yields an average meridional velocity of 1 cm/s over the deeper half of the Southern Ocean, a value that is at the limit of present direct current measurements. Local variations in space and time may be large enough to measure directly, but the mean fluxes and
Exchange Processes and Overall Budgets 41 residence times of water or materials must at present be estimated by a combination of direct and indirect methods. 1. Heat Budget of the Abyssal Water The heat extracted annually by the atmosphere must be balanced by a southward and upward flux of heat within the water column. The heat trans- fer from.sea to air (estimated from the 1966 USSR Antarctic Atlas) is about 1014 cal/s for the ocean south of the southernmost extremity of the Polar Front Zone. The heat loss is balanced by the production of cold AABW. It is possible to estimate, from flux arguments, the production rate of AABW. Assuming that the average potential temperature of the abyssal waters (defined as those below the intermediate water masses) of the World Ocean is 1.7 °C; that heat is added by the introduction of warmer water, geothermal heating, and downward diffusion of heat across the thermocline; and that all heat is removed by sea-air losses in the antarctic region, Gordon [1973] finds that the thermal balance for all abyssal waters suggests a production rate of AABW of 38 x 106m3/s. 2. Salt Budget of Antarctic Surface Water The net annual input of fresh surface water, derived from the excess of precipitation over evaporation and continental runoff, must be balanced by an upwelling of salty water to maintain the mean salinity. Superimposed on the annual values is the strong seasonal influence of the waxing and waning of sea ice. A summer salt balance study [Gordon, 1971b] of the upper 100 m of water from the Antarctic Continental Shelf to the southern extremes of the Polar Front Zone (roughly an area of 20 x 106 km2) indicates that a seasonal surface salinity variation of 0.1 °/oo requires upwelling of approximately 60 x 106 m3/s [Gordon, 1971c], in rough agreement with the mean Ekman diver- gence for this region. An annual average upwelling of 60 x 106 m3/s would transfer 14-19 kcal cm"2 yr"1 into the surface water. This agrees with the estimated annual average of 15 kcal cm"2 yr"1 heat exchange across the sea-air interface. In the winter, the salt budget is more complicated, because salt is removed from the surface water during production of AABW. By assuming that the 60 x 106 m3/s of deep-water upwelling continues at this rate all year, that the low-salinity water lost at the Polar Front removes excess sur- face water but not salt from the surface layer, and that the average salinity of the sinking cold saline shelf water is 34.65°/0o, it is possible to construct an annual salt balance of the surface water [Gordon and Taylor, 1973]. The estimates from the salt balance yield the loss rate from the upper 100 m. It is
42 Southern Ocean Dynamics POLAR FRONT I SURFACE HATER 20<1 O6 i âf 60xl06 THERMOCLINE RETURNING ABYSSAL HATERS - SOxlO6 40.-1106 CIRCUHPOLAR DEEP HATER 60xl06 FIGURE 5.2 Volume transport for "average" circumpolar north-south plane. Values from Gordon [1971b, in press] and Gordon and Taylor [1973]. not possible to extrapolate to the production rate of AABW and AAIW, because we do not yet know how the volume transport changes as these waters mix with the deeper waters, but some estimates can be made. Figure 5.2 shows in schematic fashion the average circumpolar meridi- onal volume flux obtained from the foregoing estimates of heat and salt budgets. The 10 x 106 m3/s value for returning AAIW is determined here from conservation of mass, and the 60 x 106 m3/s of deep water passing southward below the Polar Front Zone is also approximate. All the numbers are, of necessity, somewhat speculative; moreover, we remain ignorant of the processes within boxes I and II and of the processes accomplishing the heat and salt fluxes across the interface of these boxes. The values are annual circumpolar averages; large variations in time and space could drastically alter the picture. IV. RECOMMENDED PROGRAM The primary aim of the budget studies is to determine the magnitude and variability of the local exchanges. These data will be used together with information from other experiments to elucidate the characteristics and
Exchange Processes and Overall Budgets 43 dynamics of the transfer mechanisms responsible for the interactions and, finally, the influence of the Southern Ocean on global atmospheric and ocean circulation. A. GENERAL SURVEY DATA Measurements should be made in those regions where vertical and meridional fluxes of heat and salt are most active: 1. Frontal Zones There are many areas in the Southern Ocean across which marked changes are observed in water characteristics. The most commonly known of these antarctic fronts are the Antarctic Polar Front (Antarctic Convergence) and the Antarctic Divergence. The Polar Front has received most attention, since it is the formation zone of AAIW and it appears to be coincidental with the axis of the Antarctic Circumpolar Current. It is the zone separating the antarctic and subantarctic surface water masses. We know surprisingly little of the relation of the Polar Front to climatic-meteorological features and bottom topography, although Wyrtki [1961] has attempted to relate the structure of the front to the position of the maximum west wind with some success. The Polar Front is clearly related to the Antarctic Circumpolar Current; it is the thermohaline structure associated with the geostrophic flow of the current. In the Pacific sector of antarctic waters, the thermal structure of the front often displays a complex cellular structure [Wexler, 1959; Gordon, 1971a], as shown in Figure 5.3. These cells of warm water undergo rapid heat loss to the atmo- sphere and may have relevance to large-scale heat budgets and AAIW formation. We recommend a detailed survey designed to yield more information on the structure (thermal, haline, alkalinity, CO2, and nutrient distribution) of the Polar Front at various positions and times so that a determination can be made of its importance relative to other frontal areas in exchange proces- ses. Other frontal zones exist about which little is known. The principal ones are the Australasian Subantarctic Front [Burling, 1961], which occurs about 300 km north of the Polar Front in the Indian Ocean sector of ant- arctic waters; and the Weddell-Scotia Confluence [Gordon, 1967], which marks the boundary of the Weddell Gyre water (cold and relatively fresh) with the water flowing through the Drake Passage (warmer and saltier). The Con- fluence extends from the Antarctic Peninsula across the central Scotia Sea to
44 Southern Ocean Dynamics . -T.fr- -T, . JL..TT., t .. ...it, ,..jr..t. . FIGURE 5.3 Double polar front structure often observed in the thermal structure in the Pacific sector [Gordon, 1971a] . about 20° E. The vertical exchange in the Confluence zone appears to be large, since there is some indication .that the oxygen within the zone is higher at all depths than on either side. In addition to the possible relevance of this zone to vertical transfer of heat and salt, its position at the surface has a marked effect on climate. The climate of the South Sandwich Islands, which are south of the Confluence, is truly polar, but that of South Georgia, north of the Confluence, is more nearly subpolar; yet both groups are south of the Polar Front Zone. It appears that long-term movements of the Confluence could produce meridional shifting of the climatic belts. A northward shift would bring colder water (and air) farther north and probably would bring more sea ice. We recommend that each of these other frontal areas be studied to determine their relative importance in exchange processes. 2. Cyclonic Gyres The circulation pattern around Antarctica is marked by a series of large cyclonic gyres. The major gyres occur in the Weddell and Ross Sea areas; however, minor cells exist in the Bellingshausen and Amundsen Seas and the Amery Ice Shelf region. Within these gyres, the core layers, which bear an inverse relationship to the sea-surface topography, reach their shallowest levels and so may attain maximum interaction with the atmosphere. The recirculation of water within these gyres yields long residence times and may account for their colder, fresher (but denser) characteristics. The processes occurring within the gyres and the interaction with the water to the north may be important elements in vertical and meridional transfers.
Exchange Processes and Overall Budgets 45 3. Continental Margins On approaching the Continental Slope from the deep ocean, the "warm-salty" deep water changes abruptly. The water on the floor of the Continental Slope has properties closer to those of AABW than to those of deep water. The origin of the cold, but relatively fresh, water over the Con- tinental Slope does not easily fit into the schematic model shown earlier [Gordon and Tchernia, 1972]. It is possible that deep convection may occur that does not reach the sea floor. What is the magnitude of such convection, and what role does it play in larger-scale vertical transfer of heat and salt? We recommend an assessment of the role of transfer processes oc- curring within gyres and near continental margins; the initial step should be a study of existing data. 4. Sea Ice The establishment of firm budget models requires not only more in- formation on the thermohaline structure and velocity field on a variety of scales but also accurate estimates of the sea-air exchange and a better under- standing of the influence of a changing ice cover on the ocean. A sea-ice dynamics program is recommended in the 1974 CPR report Antarctic Glaci- ology: Guidelines for U.S. Program Planning, 1973-1983, Chapter 2 and Appendix D; we support that recommendation. The foregoing report also contains specific recommendations for the study of water properties beneath sea and glacial ice. Therefore, the following comments are brief and general. The extensive ice cover of Antarctica is further augmented by the highly important waxing and waning of the effective edge of the continent due to sea-ice fluctuations. Records of antarctic sea ice indicate two crucial phenomena: the first is the very large year-to-year variation in ice cover, over which are superimposed the strong seasonal oscillations; the second is the extensive ice-free regions that form near the continent early in the melting season, or possibly throughout the entire year, and that separate the open- ocean sea ice from near-coastal sea and glacial ice. The significance of these two features becomes evident on comparing the thermal characteristics of the ice-covered water with those of the ice-free water. The ice acts as an effective barrier to ocean-atmosphere exchange of radiation, sensible and latent; i.e., it adds a continental aspect to the atmo- spheric climate. What is the effect of a growing, stable, or melting ice cover on the underlying water column? This effect depends on the season and the rate of growth or melting of the sea ice. The ice insulates the water from heat gains or losses, but the water-column temperature structure will vary under the ice, since other transfer mechanisms, such as deep upwelling, may be present under the ice cover. The average temperature of the water column
46 Southern Ocean Dynamics below a stable or melting sea-ice cover may increase with time as more cir- cumpolar deep water is advected into the region and upwells or mixes verti- cally. The upwelling or vertical mixing of warmer deep water may account for the accelerated ice melting that is observed in many areas in early spring. Warming can occur even with a slowly growing ice cover when the density (at freezing) of the surface layer is increased by salinity injection and vertical mixing with the deeper warm layers increases. We know little of the meridi- onal and vertical transfer of heat in the antarctic region, especially below the sea-ice and glacial-ice covers; the thermohaline "history" of subice water column for growing and melting ice cover is thus of primary importance to budget studies and understanding of the sea-ice fluctuations. Sea ice also influences the haline component of the water column. The freezing-point brine ejected by the sea ice into the underlying water, already at or near the freezing point, results in thermohaline-induced con- vection that may reach directly to the deep ocean floor. Sea-ice formation is most active in the winter. Since lowered stability induces greater vertical flux, the water column below the forming sea ice and in the ice-free regions near Antarctica must receive attention in winter. A much-enhanced sea-air interaction occurs north of the ice fields and might be of primary concern to AAIW formation and the intensity of the Polar Front and circumpolar current. In summer and winter, the deep water upwells into the surface layer. We know little of how this upwelling proceeds, since the pycnocline is strong in every place sampled in summer and winter. The mechanisms responsible for the upward flux of the CDW into the surface layer are not know. Since this flux is not accomplished solely by diffusion (the vertical advection in- duced by*the Ekman divergence accounts for most of the necessary flux), it appears that a balance exists between the upwelling of CDW and downward erosion of the top of the CDW layer; that is, the pycnocline is eroding into the upwelling CDW. This process may be imbalanced locally. It is expected that a deepening would occur during periods of strong winds when mechanical stirring of the surface layer is strong and that shallowing would occur during calms and under stable or melting ice fields. Therefore, observations of the pycnocline should be made under a variety of environmental conditions, perhaps in each segment of a cyclone in each season. We recommend collection of data during the winter, especially below and within the sea-ice fields, noting that other seasonal data are also critical in refinement of the budget studies in the continental margins and open ocean. 5. Glacial Ice The interaction of the seawater with glacial ice, especially along the bottom of the ice shelf, is not understood. However, we do know that the
Exchange Processes and Overall Budgets 47 elevated pressure at this interface decreases the freezing point of seawater below the sea-surface value, so that the water in contact with the bottom of the ice shelf would have very low temperatures. The occurrence of tempera- tures as low as -2.26 °C near the Filchner Ice Shelf and -2.13 °C in the Ross Sea (0.2-0.3 °C below the surface freezing point) suggests that some of this water spreads northward into the open-shelf region. We can only speculate about the process occurring at the water-glacial-ice contact and about the vigor of the process in regard to the interaction with the "open" ocean. We recommend that hydrographic and meteorological measurements on the effect of glacial ice be carried out in conjunction with the various existing and proposed shelf projects and that laboratory studies of freezing- point depression as a function of pressure be supported. 6. Meteorology The presence of a permanent continental ice cap reaching to the edges of the Antarctic continent allows the polar high-pressure area to extend over the continental margins of Antarctica, producing in the coastal region a general easterly airflow that is often marked by strong katabatic winds. The coastal easterlies vary with season, with maxima at both solstices, and are bounded at the north by a climatic low-pressure trough. North of this trough are the climatic westerlies. The wind field is not steady, but rather appears to be a series of cyclones and anticyclones migrating eastward about Antarctica. The cyclones generally approach the continent by a few routine paths. The heat and water exchange between sea and air varies strongly with position within a cyclone [Zillman, 1972]. Climatic means have been calcu- lated, but they are subject to error, since the exchange can be strongly time- dependent. The neglect of the resultant nonlinearity could produce large errors in the climatic sea-air transfer determination. We recommend a continuing program for monitoring standard meteor- ological variables during all survey programs. This monitoring function could eventually be assumed by untended data stations and remote-sensing systems. B. LONG-TERM MONITORING Other than the monitoring that can be carried out with data from existing weather stations and supply ships, we do not make a specific recom- mendation for a long-term monitoring network. That plan must await the development of techniques and systems currently being tested in other oceans. However, we anticipate that the planning for such a special network might possibly begin before 1977. The technology that might be used in such a network is discussed in the next section.
48 Southern Ocean Dynamics C. TECHNOLOGY FOR LONG-TERM MONITORING Data can be collected either by the manual use of sensors, i.e., mea- surements from ships or vehicles that can maneuver on the ice fields to obtain hydrographic data through the ice and in ice-free pockets, or by remote sensing from satellite or aircraft. The first method allows flexibility in experi- mental procedures, and the second allows data gathering for long periods and in regions and seasons when no manned vessel or vehicle can be present. From the manned vessels or vehicles, traditional measurements should be carried out in the entire water column, with particular emphasis on the upper kilo- meter. Attention to the microstructure and middle-scale structure is necessary, especially in ice fields. Since measurements in the ice fields should be made over the annual history of the ice cover, a combination of ships and over-the-ice vehicles will be needed. Unmanned stations of various typesâdrifting, moored with a surface float, or "locked" in the iceâmight be used to obtain long-term measurement of meteorological parameters at a number of distances from the sea (or ice) surface, as well as measurements of the water temperature and salinity at a number of levels in the water column. Such measurements can be used to monitor the near-surface heat storage, to refine the sea-air heat flux, and, by observing drift of the buoys or by measuring the current from the moored systems, to determine the response of the ocean to the wind. Subsurface moored buoys can be used to obtain long-term ther- mohaline and current measurements below the sea ice. It is possible that buoys frozen into the pack ice fields would be more useful, since they could give meteorological data and relay information to satellites. Supply aircraft flying between New Zealand and McMurdo should routinely measure sea temperature with infrared thermometers. Although cloud cover would often negate such data, enough "holes" can be found to at least study the clear-sky periods. Microradiowave frequency can also be used to obtain crude temperature data through the cloud cover but would, more significantly, yield sea-ice configuration information. Satellite observation of the oceans' irradiance should also be carried out. D. SUMMARY OF RECOMMENDED PROGRAM Tables 5.1 and 5.2 summarize the experiments and goals and show how the recommended program would fit into a ten-year time scale.
Exchange Processes and Overall Budgets 49 TABLE 5.1 Recommended Program Structure Specific Goals Measure energy exchange between ocean and atmosphere. Reduce logistics costs of long-term data collection. Relate ocean-atmosphere heat exchanges to subsur- face water mass formation and atmospheric circulation variability. Isolate and understand exchange processes, e.g., determine relation between subsurface water-mass for- mation and ocean-atmosphere heat exchanges, for para- meterization into global circulation models. Exchange Processes and Overall Budgets Experiments and Goals Proposed Experiments and Theory Monitoring Experiments * Ice cover variability from microwave imagery from satellites. * Heat storage in upper layers from temperature profiles reported by drifters. * Surface temperature and properties by remote sensing. * Long-term variability of the front from remote sensing. Collect planning data across frontal zones. Organize collection of upper layer data from supply and weather ships. Refine existing overall energy budgets with new and incoming data Use input from CUE, NORPAX, and JASIN to formulate upper layer models relevant to Southern Ocean. Review and formulate adequate frontal-zone models.
50 Southern Ocean Dynamics TABLE 5.2 RECOMMENDED PROGRAM STRUCTURE Exchange Processes and Overall Budgets Time-Phased Diagram 1973 - 1976 |Time Frame \ 1976 - 1979 1979 - 1982 CONTINUAL PLANNING AND REVIEW Moni toring Experiments ⢠Ice cover variability (satellite) ⢠Surface Temperature and properties (satellite) ⢠Heat storage In upper layers (drifters) ⢠Long-term variability of front (satellite) Begin 1 Survey ⢠Collect planning data across frontal zones ⢠Detailed frontal survey ⢠Collect supply and weather ship data [Theory ⢠Refine existing budgets with new and incoming data ⢠Use input from other experiments to formu- late Southern Ocean models ⢠Review and formulate adequate frontal zone models Begin Begin Begin Begin "Begin Begin - Begin Establish monitoring for FGGE collaboration Merge into Internationl Climate Research Effort REFERENCES Burling, R. W. 1961. Hydrology of circumpolar waters south of New Zealand. New Zealand Dep. Sci Ind. Res. Bull. 143, Memoir 10, 9-61. Committee on Atmospheric Sciences, National Research Council. 1973. Weather and Climate Modification: Problems and Progress, p. xiii. National Academy of Sci- ences, Washington, D.C. Gordon, A. L. 1967. Structure of Antarctic waters between 20° W and 170° W. In Antarctic Map Folio Series 6, V. Bushnell, ed. American Geographical Society, New York. Gordon, A. L. 1971c. Recent physical oceanographic studies of Antarctic waters, pp. 609-629 in Research in the Antarctic, L. O. Quam, ed. American Association for the Advancement of Science, Washington, D.C. Gordon, A. L. 1971b. Oceanography of Antarctic waters, pp. 169-203 in Antarctic Oceanology I, J. L. Reid, ed. Antarctic Research Ser. Vol. 15. American Geo- physical Union, Washington, D.C.
Exchange Processes and Overall Budgets 51 Gordon, A. L. 1971a. Antarctic Polar Front Zone, pp. 204-221 in Antarctic Oceanology I, }. L. Reid, ed. Antarctic Research Ser. Vol. 15. American Geophysical Union, Washington, D.C. Gordon, A. L. 1973. A general ocean circulation. In Proceedings of the Symposium on Numerical Models of Ocean Circulation, October 1972 (National Academy of Sciences). Durham, N.H. Gordon, A. L., and H. Taylor. 1973. Heat and salt balances within the world ocean. In Proceedings of the Symposium on Numerical Models of Ocean Circulation, October 1972 (National Academy of Sciences). Durham, N.H. Gordon, A. L., and P. Tchernia. 1972. Waters of the continental margin off Adelie coast, Antarctica, pp. 59-69 in Antarctic Oceanology II: The Australian-New Zealand Sector, D. E. Hayes, ed. Antarctic Research Ser. Vol. 15. American Geophysical Union, Washington, D.C. Mosby, H. 1934. The waters of the Atlantic Antarctic Ocean. Sci. Res. Norwegian Ant. Exped. 1927-1928 Rep. 11, Norske Videnskaps-Akad. Wexler, H. 1959. The Antarctic convergence or divergence? pp. 107-120 in Atmosphere and the Sea in Motion, B. Bolin, ed. Rockefeller Institute Press, New York. Wyrtki, K. 1961. The Antarctic Circumpolar Current and the Antarctic Polar Front. Deut. Hydr. Z. 13, 153-173. Zillman, J. 1972. Solar radiation and sea-air interaction south of Australia, pp. 11-40 in Antarctic Oceanology II: The Australian-New Zealand Sector, D. E. Hayes, ed. Antarctic Research Ser. Vol. 19. American Geophysical Union, Washington, D.C.
