Regional Environmental Assessment of the Northern Mid-Atlantic Ridge Document prepared by the Atlantic REMP project to support the ISA Secretariat in facilitating the development of a Regional Environmental Management Plan for the Area in the North Atlantic by the International Seabed Authority Supported by Legal Notice This document has been prepared for the European Commission however it reflects the views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained therein Disclaimer by ISA secretariat: The views expressed are those of the author(s) and do not necessarily reflect those of the International Seabed Authority. Regional Environmental Assessment of the Northern Mid-Atlantic Ridge Authorship The primary authors for each chapter are listed below Geological Overview of the Mid-Atlantic P.P.E. Weaver, Seascape Consultants Ltd Ridge Contract areas and the mining process P.P.E. Weaver, Seascape Consultants Ltd Physical Oceanography of the North Atlantic A.C. Dale, Scottish Association for Marine Science Biology Chapters R. E. Boschen-Rose, Seascape Consultants D.S.M. Billett, Deep Seas Environmental Solutions Ltd A. Colaço, U. Azores D. C. Dunn, Duke University T. Morato, U. Azores I. G. Priede, U. Aberdeen Cumulative impacts D. Jones, NOC D.S.M. Billett, Deep Seas Environmental Solutions Ltd Citation: Weaver, P.P.E., Boschen-Rose, R. E., Dale, A.C., Jones, D.O.B., Billett, D.S.M., Colaço, A., Morato, T., Dunn, D.C., Priede, I.G. 2019. Regional Environmental Assessment of the Northern Mid-Atlantic Ridge. 229 pages This document benefitted from the invaluable reviews of Marina Carreiro-Silva, U. Azores Gordon Paterson, Natural History Museum, Uk Jose Angel Alvarez Perez, Universidade do Vale do Itajaí – UNIVALI, Brazil Piers Dunstan, CSIRO, Australia Cindy van Dover, Duke University, USA With additional comments from participants to the ISA Workshop on Regional Environmental Management Plan for the Area of the Northern Mid-Atlantic Ridge (MAR), at the University of Évora, Portugal, (25-29 November 2019) Cover Fig SRTM15+: GLOBAL BATHYMETRY AND TOPOGRAPHY AT 15 ARCSECONDS (available from: https://topex.ucsd.edu/WWW_html/srtm15_plus.html) Reference Tozer, B, Sandwell, D. T., Smith, W. H. F., Olson, C., Beale, J. R., & Wessel, P. ( 2019). Global bathymetry and topography at 15 arc sec: SRTM15+. Earth and Space Science, 6, 1847– 1864. https://doi.org/10.1029/2019EA000658 Page 1 Regional Environmental Assessment of the Northern Mid-Atlantic Ridge TABLE OF CONTENTS 1. ABBREVIATIONS .....................................................................................................................................6 2. DOCUMENT PURPOSE AND SCOPE .........................................................................................................8 2.1 REFERENCES ............................................................................................................................................ 9 3. AREA OF CONSIDERATION .................................................................................................................... 10 4. GEOLOGICAL OVERVIEW OF THE MID-ATLANTIC RIDGE OF THE NORTH ATLANTIC ............................... 11 4.1 DESCRIPTION OF THE MID-ATLANTIC RIDGE ................................................................................................. 11 4.2 SEAMOUNTS .......................................................................................................................................... 18 4.3 HYDROTHERMAL VENTS AND FORMATION OF ORE BODIES ............................................................................... 20 4.4 RELATIONSHIP OF ACTIVE TO INACTIVE VENT SITES ......................................................................................... 24 4.5 LOCATION OF VENT SITES ALONG THE MAR ................................................................................................. 25 4.6 REFERENCES .......................................................................................................................................... 29 5. CONTRACT AREAS AND THE MINING PROCESS ..................................................................................... 30 5.1 EXISTING ISA CONTRACT AREAS ON THE NORTHERN MID-ATLANTIC RIDGE ........................................................ 30 5.2 RESOURCE POTENTIAL.............................................................................................................................. 32 5.3 DETECTION OF ORE BODIES ....................................................................................................................... 33 5.4 MINING SCENARIO .................................................................................................................................. 35 5.5 POTENTIAL AREAS OF IMPACT .................................................................................................................... 37 5.6 REFERENCES .......................................................................................................................................... 39 6. PHYSICAL OCEANOGRAPHY OF THE NORTH ATLANTIC.......................................................................... 44 6.1 INTRODUCTION AND SCOPE ....................................................................................................................... 44 6.2 LARGE-SCALE CIRCULATION ....................................................................................................................... 44 6.2.1 Overview ....................................................................................................................................... 44 6.2.2 Surface layer currents ................................................................................................................... 45 6.2.3 Intermediate layer currents .......................................................................................................... 47 6.2.4 Deep layer currents ....................................................................................................................... 48 6.3 DISTRIBUTION OF WATER PROPERTIES ......................................................................................................... 49 6.3.1 Temperature and salinity .............................................................................................................. 51 6.3.2 Oxygen .......................................................................................................................................... 52 6.3.3 Turbidity ........................................................................................................................................ 53 6.4 THE LOCAL FLOW ENVIRONMENT OF THE MAR ............................................................................................. 53 6.4.1 The axial valley – stratification, mixing and compensating flows ................................................ 53 6.4.2 The ridge flanks – mixing-driven upslope flow .............................................................................. 54 6.4.3 Sills – intensified hydraulic flows and mixing ................................................................................ 54 6.4.4 Local tidal processes – internal tides, lee waves and bores .......................................................... 55 6.4.5 Influence of natural hydrothermal vents and plumes ................................................................... 56 Page 2 Regional Environmental Assessment of the Northern Mid-Atlantic Ridge 6.4.6 General comments on the nature of the small-scale physical environment ................................. 57 6.5 VARIABILITY ........................................................................................................................................... 57 6.5.1 Basin scale..................................................................................................................................... 57 6.5.2 Mesoscale ..................................................................................................................................... 57 6.6 INFLUENCE OF THE PHYSICAL ENVIRONMENT ON MINING ACTIVITIES ON THE MAR ............................................... 58 6.6.1 Plume behaviour ........................................................................................................................... 58 6.6.2 Large scale dispersion from the MAR ........................................................................................... 59 6.7 REFERENCES .......................................................................................................................................... 59 7. CUMULATIVE IMPACTS ......................................................................................................................... 65 7.1 INTRODUCTION ...................................................................................................................................... 65 7.2 CONSIDERATIONS FOR POTENTIAL CUMULATIVE IMPACTS ................................................................................ 66 7.3 TYPES OF CUMULATIVE IMPACTS ................................................................................................................ 68 7.3.1 Multiple mining operations ........................................................................................................... 68 7.3.2 Fishing and other harvesting .......................................................................................................