Although there have been significant advances in our ability to describe and model the Earth System, our understanding of geologic, oceanic and atmospheric processes in the Indian Ocean is still rudimentary in many respects. This is largely because the Indian Ocean remains under-sampled in both space and time, especially compared to the Atlantic and Pacific oceans. The situation is compounded by the Indian Ocean being a dynamically complex and highly variable system under monsoonal influence. Many uncertainties remain in terms of how geologic, oceanic and atmospheric processes affect climate, extreme events, marine biogeochemical cycles, ecosystems and human populations in and around the Indian Ocean. There are also growing concerns about food security in the context of global warming and of anthropogenic impacts on coastal environments and fisheries sustainability. These impacts include sea level rise, which leads to coastal erosion, loss of mangroves, and loss of biodiversity. There is a pressing need for ecosystem preservation in the Indian Ocean for both tourism and fisheries. More than 50 years ago the Scientific Committee on Oceanic Research (SCOR) and the Intergovernmental Oceanographic Commission (IOC) of UNESCO motivated one of the greatest oceanographic expeditions of all time: the International Indian Ocean Expedition (IIOE). In the 50 years since the IIOE, fundamental changes have taken place in geological, ocean and atmospheric sciences. These have revolutionized our ability to measure, model, and understand the Earth System. Thanks to these technological developments we can now study how the ocean changes across a wide range of spatial and temporal scales, and how these fluctuations are coupled to the atmosphere and topography. Moreover, compared to the IIOE era, which relied almost exclusively on ship-based observations, new measurement technologies—in combination with targeted and well-coordinated field programs—provide the capacity for a much more integrated picture of Indian Ocean variability. In addition, improved communication through the World Wide Web allows much broader engagement of the global scientific community. SCOR, IOC, and IOGOOS are coordinating a new phase of international research focused on the Indian Ocean beginning in late 2015 and continuing through 2020. The goal is to assist ongoing research and stimulate new initiatives in this time frame as part of the Second International Indian Ocean Expedition - IIOE-2. The Mission of IIOE-2 is: To advance our understanding of the Indian Ocean and its role in the Earth System in order to enable informed decisions in support of sustainable development and well-being of humankind. In order to fulfill this mission, IIOE-2 will need to increase our knowledge of interactions between geologic, oceanic and atmospheric processes thatgive rise to the complex physical dynamics of the Indian Ocean region, and determine how those dynamics affect climate, extreme events, marine biogeochemical cycles, ecosystems and human populations. This understanding is required to predict the impacts of climate change, pollution, and increased fish harvesting on the Indian Ocean and its surrounding nations, as well as the influence of the Indian Ocean on other components of the Earth System. New understanding is also fundamental to policy makers for the development of sustainable coastal zone, ecosystem, and fisheries management strategies for the Indian Ocean. Other goals of IIOE-2 include helping to build research capacity and improving availability and accessibility of oceanographic data from the region. The IIOE-2 Science Plan is structured around six scientific themes. Each of these include a set of questions that need to be addressed in order to improve our understanding of the physical forcing that drives variability in marine biogeochemical cycles, ecosystems and fisheries in the Indian Ocean and develop the capacity to predict how this variability will impact human populations in the future. It is also important to emphasize that most of these questions are relevant to open ocean, coastal and marginal sea environments. Theme 1: Human Impacts (How are human-induced ocean stressors impacting the biogeochemistry and ecology of the Indian Ocean? How, in turn, are these impacts affecting human populations?) • Theme 2: Boundary current dynamics, upwelling variability and ecosystem impacts (How are marine biogeochemical cycles, ecosystem processes and fisheries in the Indian Ocean influenced by boundary currents, eddies and upwelling? How does the interaction between local and remote forcing influence these currents and upwelling variability in the Indian Ocean? How have these processes and their influence on local weather and climate changed in the past and how will they change in the future?) • Theme 3: Monsoon Variability and Ecosystem Response (What factors control present, past and future monsoon variability? How does this variability impact ocean physics, chemistry and biogeochemistry in the Indian Ocean? What are the effects on ecosystems, fisheries and human populations?) • Theme 4: Circulation, climate variability and change (How has the atmospheric and oceanic circulation of the Indian Ocean changed in the past and how will it change in the future? How do these changes relate to topography and connectivity with the Pacific, Atlantic and Southern oceans? What impact does this have on biological productivity and fisheries?) • Theme 5: Extreme events and their impacts on ecosystems and human populations (How do extreme events in the Indian Ocean impact coastal and open ocean ecosystems? How will climate change impact the frequency and/or severity of extreme weather and oceanic events, such as tropical cyclones and tsunamis in the Indian Ocean? What are the threats of extreme weather events, volcanic eruptions, tsunamis, combined with sea level rise, to human populations in low-lying coastal zones and small island nations of the Indian Ocean region?) • Theme 6: Unique geological, physical, biogeochemical, and ecological features of the Indian Ocean (What processes control the present, past, and future carbon and oxygen dynamics of the Indian Ocean and how do they impact biogeochemical cycles and ecosystem dynamics? How do the physical characteristics of the southern Indian Ocean gyre system influence the biogeochemistry and ecology of the Indian Ocean? How do the complex tectonic and geologic processes, and topography of the Indian Ocean influence circulation, mixing and chemistry and therefore also biogeochemical and ecological processes?)

Programmatic Linkages This IIOE-2 Science Plan has been developed with the sponsorship of the Scientific Committee on Oceanic Research (SCOR). The plan relies significantly on regional input from the IIOE-2 Reference Group meetings sponsored by the Intergovernmental Oceanographic Commission (IOC) of UNESCO (see Appendix II). The IIOE-2 will coordinate with international research efforts such as the Integrated Marine Biogeochemistry and Ecosystem Research (IMBER) program and its Sustained Indian Ocean Biogeochemistry and Ecosystem Research (SIBER) program, the Surface Ocean – Lower Atmosphere Study (SOLAS), the Indian Ocean Global Ocean Observing System (IOGOOS), GEOTRACES (a program to improve the understanding of biogeochemical cycles and large-scale distribution of trace elements and their isotopes in the marine environment), the Global Ocean Ship-Based Hydrographic Investigations Program (GO-SHIP), the International Ocean Discovery Program (IODP), InterRidge (an international project that promotes interdisciplinary, international studies of oceanic spreading centers), the Year of the Maritime Continent (YMC) research initiative, and others. IIOE-2 will also leverage several coastal and open-ocean monitoring programs in the Indian Ocean. These include the CLIVAR and GOOS-sponsored Indian Ocean Observing System (IndOOS), Australia’s Integrated Marine Observing System (IMOS), the Southern Ocean Observing System (SOOS) and several regional GOOS programs. To develop a broader understanding of the Indian Ocean ecosystem IIOE-2 will coordinate its efforts with the Western Indian Ocean Marine Science Association (WIOMSA), the South African Network for Coastal and Oceanic Research (SANCOR), the Strategic Action Programme Policy Harmonization and Institutional Reforms (SAPPHIRE) project, the Bay of Bengal Large Marine Ecosystem (BOBLME) project, and the EAF-Nansen project (Strengthening the Knowledge Base for and Implementing an Ecosystem Approach to Marine Fisheries in Developing Countries). As IIOE-2 develops it is envisaged that the number of participants, institutes and programs involved will increase. IIOE-2 will provide the innovation, direction and coordination required to build a critical mass of multidisciplinary science and scientists to mount this ambitious and globally important expedition. Legacy The motivation, coordination and integration of Indian Ocean research through IIOE-2 will advance knowledge, increase scientific capacity, and enable international collaboration in an under-sampled, poorly understood, yet important region. IIOE-2 will promote awareness of the significance of Indian Ocean processes and enable a major contribution to their understanding, including the impact of Indian Ocean variability and change on regional ecosystems, human populations, and global climate. The legacy of IIOE-2 will be to establish a firmer foundation of knowledge on which future research can build and on which policy makers can make better-informed decisions for sustainable management of Indian Ocean ecosystems and mitigation of risk to Indian Ocean rim populations. IIOE-2 will leverage and strengthen SCOR and IOC by promoting coordinated international, multidisciplinary research among both developed and developing nations, hence increasing scientific capacity and infrastructure within the Indian Ocean rim and neighboring nations. The success of IIOE-2 will be gauged not just by how much it advances our understanding of the complex and dynamic Indian Ocean system, but also by how it contributes to sustainable development of marine resources, environmental stewardship, ocean and climate forecasting, and training of the next generation of ocean scientists from the region. If this vision of success is realized, IIOE-2 will leave a legacy at least as rich as the original expedition.