Hydrology of Circumpolar Waters South of New Zealand
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ISSN 2538-1016; 10 NE\\' ZEALAND DEPARTMENT OF SCIENTIFIC AND I�"DC TRIAL RESEARCH BULLETIN 143 HYDROLOGY OF CIRCUMPOLAR WATERS SOUTH OF NEW ZEALAND by R. W. BURLING New Zealand Oceanographic Institute Wellington New Zealand Oceanographic Institute Memoir No. 10 1961 This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/3.0/ { l'/,otogr(IJ>lt by T. J.loyd HM ZS Hawea in the Southern Ocean, December I 956. Fronti1piece This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/3.0/ NEW ZEALAND DEPARTMENT OF SCIENTIFIC AND INDUSTRIAL RESEARCH BULLETIN 143 HYDROLOGY OF CIRCUMPOLAR W.Lt\.TERS SOUTH OF NEW ZEALAND by R. W. BURLING New Zealand Oceanographic Institute Wellington New Zealand Oceanographic Institute Memoir No. 10 1961 This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/3.0/ FOREWORD lN December 1956 and January 1957, the N.Z. Oceanographic Institute carried out oceanographic observations in Antarctic and Subantarctic waters from the frigates HM ZS Pukaki and ffawea. This undertaking initiated a series of cruises to southern waters during the International Geophysical Year. During the voyage the principal objectives were hydrological observations, particularly in the region of the Antarctic Convergence and, on the return to New Zealand waters, in the region of the Subtropical Convergence. The sampling also included surface plankton tows and sediment and core sampling. Some of the hydrological results ( 14C activities of bulk water samples from depth) have been interpreted and published elsewhere. Preliminary analysis of the results reported here has guided subsequent work by the Institute carried out in the Southern Ocean. Preliminary editing has been carried out by Dr D. E. Hurley and Mrs P. M. Cullen. The material has been finally edited for publication by Mr M. O'Connor, Information Bureau, D.S.LR. J. W. BRODIE, Director, New Zealand Oceanographic Institute. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/3.0/ CONTENTS Page No. INTRODUCTION 9 RESULTS OF THE Pukaki-Hawea CRUISES IN SOUTHERN WATERS Collection of Data JO Surface Characteristics .. JO Ambiguities in the Construction of Isolines JO Bathythermograph Sections 11 Station Data ll REVIEW OF PREVIOUS WORK ON WATER MASSES AND THEIR BOUND- ARIES SOUTH OF NEW ZEALAND 14 HYDROLOGICAL FEATURES IN TH£ ANTARCTIC AND SUBANTARCTJC REGIONS Subsurface Waters 15 The Antarctic Convergence 16 Antarctic Surface Water .... I 9 Australasian Subantarctic Water and Circumpolar Subanlarctic Water 20 Warm Saline Water South of New Zealand 23 Australasian Subantarctic Front . ...... 24 General Water Movements Over the Campbell Plateau 34 THE SUBTROPICAL CONVERGENCE REGION Introduction 25 Atlantic and Western Indian Oceans 26 East Indian Ocean and South of Australia . 27 East of New Zealand 28 West of New Zealand ...... 30 South of New Zealand ...... 33 Extent of the Subtropical Convergence Region 36 THE SOUTHLAND FRONT General Description 37 Water Movements near the Southland Front 38 A MIXING PROCESS AT THE SUBTROPICAL CONVERGENCE 42 EDDIES, DIVERGENCE, AND STREAMS An Eddy in Antarctic Waters 44 Divergence and the Antarctic Convergence 46 A Free Stream Current in Subantarctic Waters 49 CURRENTS IN SUBTROPICAL AND SUBANTARCTJC WATERS Tasman Current 51 Southland Current and Canterbury Current 5 J East Cape Current 52 The Circumpolar Current 52 Drift Currents 52 A Constricted Current 53 Bounty-Campbell Gyral . 54 Free Stream Current 54 Origin of the Southland Front 54 SUMMARY The Subtropical Convergence Region 56 Subantarctic Water 56 The Southland Current and Southland Front 56 Constricted Current 56 Australasian Subantarctic Front 57 Free Stream Current 57 Bounty-Campbell Gyral 57 �� � Divergence 57 Antarctic Intermediate Current 57 Mixing Processes 57 ACKNOWLEDGMENTS 58 REFERENCES 59 APPENDIX A STATION DATA Pukaki Stations 62 Hawea Stations 64 INDEX 66 This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/3.0/ FIGURES Fig. No. Page No. 1. Tracks of Pukaki and Hawea, bathymetry, and station positions 12 2. Surface isotherms and isohalines 13 3. Temperature sections from bathythermograph observations north of Lat. 56°S 17 4. Temperature sections from bathythermograph observations south of Lat. 56°S 21 5. Temperature sections from bathythermograph observations between Lat. 65° S ° and Lat. 63 S 25 6. Temperature sections from bathythermograph observations between the Chatham Islands and Dunedin 27 7. Vertical section of salinity and density distributions between NZOI Stations C 10 and C 29 29 8. Vertical section of temperature distribution between NZOI Stations B 28 and B 36 31 9. Vertical section of salinity distribution between NZOI Stations B 28 and B 36 31 I 0. Vertical section of density between NZOI Stations B 28 and B 36 33 11. Vertical section of temperature and salinity between Macquarie and Auck- land Islands 35 .12. Water characteristics at constant depths across the Subtropical Convergence 35 13. Observed positions of the Subtropical Convergence Region 37 .14. T-S characteristics, NZOI Stations C 10 to C 29 . 39 15. T-S characteristics, Discovery 11 Stations. South of Atlantic and Western Indian Ocean, and Ob Stations south of Central Indian Ocean . 41 16. T-S characteristics of Discovery ll and Ob Stations. South of the Eastern Indian Ocean and Tasmania 43 17. T-S characteristics of Discovery II, Oh, and Derwent Hunter Stations in and south of the Tasman Sea and South of New Zealand 45 l 8. T-S characteristics of Pukaki and Discovery ll Stations in and south of the Tasman Sea and south of New Zealand 47 19. Comparison of the observed range of Subtropical Convergence Region with mean monthly isotherms for February and August 49 -PLATES Facing page Frontispiece. HM ZS Hawea in the Southern Ocean, December 1956 I. Bathythermograph observations from HM ZS Pukaki 18 2. Reading reversing thermometers on board HMNZS P11kaki 18 3. Bergs south of the Antarctic Convergence 34 4. Lowering the 14C Sampler, Station B 28 34 CHARTS J. (in folder) Currents in the Sovthern New Zealand Region. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/3.0/ HYDROLOGY OF CIRCUMPOLAR WATERS SOUTH OF NEW ZEALAND INTRODUCTION This paper provides a description and interpretation of hydrological data obtained by the New Zealand Oceanographic Institute during cruises on the RNZN frigates Pukaki and Hawea into Antarctic waters during December 1956 and January 1957. These cruises formed part of the Institute's contribution to the International Geophysical Year programme. Some results of this investigation suggested the more detailed study of waters in and close to the northern Subantarctic region, using also data from the RRS Discovery 11, the Russian RV Ob, and the Australian FRV Derwent Hunter. Hypotheses are then offered concerning the nature of currents in the Southern Ocean, south of New Zealand. Hydrological observations carried out from Pukaki and Hawea were designed to sample sur face temperature and salinity over the regions traversed and temperatures to 250 m by bathy thermograph. During the return voyages serial temperatures and salinity observations to greater depths were made through the Antarctic and Subtropical Convergences and over the Campbell Plateau. J. W. Brodie, H. M. Pantin, and R. W. Burling conducted the oceanographic work from Pukaki and R. P. Willis, that from Hawea. RESULTS OF THE "PUKAKI"-"HAWEA" CRUISES IN SOUTHERN WATERS From 17 to 19 December 1956 the frigates Island to the pack-ice, near Scott Island. Endea HMNZS Pukaki and HMNZS Hawea escorted the vour continued her southward voyage to McMur Royal Yacht Britannia, with H.R.H. the Duke of do Sound, while the two frigates returned to Edinburgh on board, from Lyttelton to Waitangi, New Zealand along the meridians 169° E (Pu Chatham Islands. The frigates left Waitangi on the 0 evening of 19 December and proceeded to Dune kaki) and 180. (Hawea) (fig. 1) Hawea returned din. They then accompanied HMNZS Endeavour to Wellington on 3 January 1957 and Pukaki to between 22 and 27 December from near Stewart Lyttelton on 4 January. 9 This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/3.0/ Cou.Ecr10N or DATA this instrument is given by Hamon as +0·04°/ 00, but the observed consistency of the measurements The temperature of sea water entering the en on the sub-standard suggests that they are correct gine-room intakes at a depth of 4 m, was con to ±0 030/ tinuously recorded by thermograph throughout 00 . the voyages on both frigates. The surface thermo Nine serial stations were worked on Pukaki graph readings on Pukaki were calibrated from at N.Z.O.I. Stations B 28 to B 36 (fig. 1). Ob reversing thermometer readings at nine stations. served temperatures and salinities and computed The average Hawea temperatures were then cor values of at are given in table 1. rected to agree with average Pukaki temperatures, Two water samples for 14C analysis were col measured while the ships were stationed less than lected from Pukaki. These have been reported 5 miles apart (see fig. 1).