Wallace LM, Townend J, Stevens C, Kellett RL, De Souza J, Giorli G, Hillman JIT, Holden C, Howe B, Leduc D, Lindsey N, Mountjoy J, Power WL, Warren-Smith E. 2021. Chatham Islands cabled observatory science opportunities: workshop 23–24 February 2021 summary report. Lower Hutt (NZ): GNS Science. 70 p. (GNS Science report; 2021/26). doi:10.21420/K1BM-RP28.
Abstract:
Our ability to address many key questions regarding physical oceanography, plate boundary processes and marine biodiversity, and to undertake geohazards monitoring in the New Zealand region, is greatly hampered by the lack of access to real-time, continuous offshore monitoring
of a range of key observables beneath our oceans, which comprises >95% of our Exclusive Economic Zone (EEZ). Developing the ability to monitor geological, biological and oceanographic processes within our EEZ is required to better understand the hazard and risk posed to New Zealand’s citizens and our economy by our offshore tectonic plate boundaries and the impact of future climate change on fisheries, weather, marine biodiversity and ocean circulation.
To discuss the possibilities for future permanent offshore monitoring, a two-day workshop on ‘Scientific and monitoring priorities for cabled infrastructure offshore New Zealand’ was held at GNS Science in Lower Hutt, New Zealand, on 23–24 February 2021. The workshop brought together the New Zealand Geoscience and Ocean Science communities, international experts and other interested stakeholders to discuss the scientific and geohazards monitoring benefits of instrumented fibre-optic cables offshore of New Zealand. Excellent presentations from both international and New Zealand invited speakers achieved the important goal of laying the framework for the current technological capabilities in offshore cabled monitoring and set the stage for discussion of the key scientific questions that can be addressed in New Zealand with such infrastructure (see Appendix 1 for workshop schedule). More than 75 participants from more than 25 institutions in eight different countries attended the workshop (see Appendix 2 for participant list). Approximately 40 participants attended in person, while other attendees (particularly those from overseas) joined the workshop online. The discussion addressed ways of leveraging the opportunities presented by a proposed fibre-optic telecommunications cable extending ~800 km from the east coast of the New Zealand mainland to the Chatham Islands. Presentations were also made by international experts on developments in seafloor monitoring technologies and offshore cabled networks, promoting extensive discussion of their advantages and disadvantages. The primary scientific questions and geohazard monitoring priorities that would benefit from permanent, offshore instrumentation were discussed, as well as hazards that could be faced by a cable transecting alternative routes.
This report summarises the main findings and conclusions of the workshop and background information necessary for considering the development of permanent offshore observing capability in New Zealand. We present the pros and cons of potential routes for a cable to the Chatham Islands from a scientific and technical perspective. A primary conclusion of the workshop, and a recommendation of this report, is that a hybrid cable design incorporating both ‘in-line’ sensors and external sensors connected to branching units, plus fibre strands usable for distributed acoustic sensing (DAS), would provide the best balance between the oceanographic, geophysical and geohazards monitoring benefits of offshore scientific infrastructure. This approach to the cable design would future-proof the cable and its sensor payloads, maximising the return on investment as technology improves in decades to come, while ensuring that the scientific components did not compromise the cable’s primary telecommunications mission. Many of the scientific sensing capabilities that we discuss would also enable more comprehensive monitoring of cable health and potential risks posed to the cable. Incorporating branching units to which external instrument packages can be attached would ensure that instruments can be replaced and new sensors added as technology improves. Incorporating additional dark fibres (for DAS and related applications) would enable New Zealand to take full advantage of rapidly evolving capabilities in this frontier technique at modest additional cost. SMART instrumentation installed at repeater nodes would provide long deep-ocean temperature time series, as well as seafloor pressure and seismological sensing capability that can contribute to tsunami and earthquake early warning capabilities and provide proof-of-concept for similar projects elsewhere in the southwest Pacific region. Further discussion and research will be required among smaller working groups to finalise an optimal design for integrating science capability into a telecommunications cable that maximises scientific and monitoring benefits of such a cable in the New Zealand context.
Different cable routes would offer different opportunities and pose different challenges. In light of the workshop discussions, this report identifies a route option extending south from Gisborne for ~150 km (paralleling the east coast) before turning southeastward to the Chatham Islands as providing the greatest benefit for scientific (geophysical and oceanographic aims) and geohazard monitoring purposes. The incorporation of scientific sensor payloads in a cable extending to the Chatham Islands would offer a unique opportunity for New Zealand to lead the way in establishing critical multi-disciplinary offshore observing capability by leveraging telecommunications infrastructure and investment. (auth)
