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Toward an Interdisciplinary Ocean Observing System in 2025

Eric D’Asaro*


The changes in our ability to observe the physical aspects of the ocean over the last 30 years have been remarkable. I can now go to the Internet and get estimates of the ocean stratification, currents and atmospheric forcing anywhere in the world. These products are constructed primarily from climatologies, Argo float data, satellite observations and numerical model systems that assimilate both oceanographic and meteorological data. These estimates and the associated predictions are imperfect in many ways, but their skill demonstrates the remarkable success of physical oceanography in measuring and understanding the dynamics of ocean circulation. This observing system is dramatically changing the way that physical oceanography is conducted and will continue to do so. I hope, and expect, that similar changes will occur in the study of ocean biogeochemical processes by 2025. This note outlines my thoughts on the driving forces toward this change, possible pitfalls and the resulting social changes in the field. I will focus on the autonomous ocean component, since that’s what I know, while ignoring the important satellite and modeling components.

The key force driving this change will be sensors. A crucial development behind physical oceanography’s switch from water sampling to electronic sensors has been Seabird Electronics sustained efforts to honestly meet the WOCE standards for CTD accuracy. As a result, relatively inexpensive temperature and salinity measurements can be made by

*

Applied Physics Laboratory, University of Washington



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Toward an Interdisciplinary Ocean Observing System in 2025 Eric D’Asaro* The changes in our ability to observe the physical aspects of the ocean over the last 30 years have been remarkable. I can now go to the Internet and get estimates of the ocean stratification, currents and atmospheric forcing anywhere in the world. These products are constructed primarily from climatologies, Argo float data, satellite observations and numeri- cal model systems that assimilate both oceanographic and meteorologi- cal data. These estimates and the associated predictions are imperfect in many ways, but their skill demonstrates the remarkable success of physical oceanography in measuring and understanding the dynamics of ocean circulation. This observing system is dramatically changing the way that physical oceanography is conducted and will continue to do so. I hope, and expect, that similar changes will occur in the study of ocean biogeochemical processes by 2025. This note outlines my thoughts on the driving forces toward this change, possible pitfalls and the resulting social changes in the field. I will focus on the autonomous ocean compo- nent, since that’s what I know, while ignoring the important satellite and modeling components. The key force driving this change will be sensors. A crucial develop- ment behind physical oceanography’s switch from water sampling to electronic sensors has been Seabird Electronics sustained efforts to hon- estly meet the WOCE standards for CTD accuracy. As a result, relatively inexpensive temperature and salinity measurements can be made by *Applied Physics Laboratory, University of Washington 11

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12 OCEANOGRAPHY IN 2025 almost any observational group with accuracies sufficient for all but the most demanding applications. There is a vast potential for similar sen- sor development in chemical and biological oceanography, particularly given the large number of potentially measurable quantities. At present, sensors for oxygen, optical properties, and some nutrients are becoming sufficiently accurate and easy to use. Carbon system sensors will follow shortly. In the longer term we can hope, for example, for genomic mea- surements of species distributions. The second key element is platforms. The current technology of Argo floats is quite mature; gliders are rapidly maturing. Given the potentially large number of biogeochemical sensors, there is probably a need for vehicles with a larger payload capability than the current Argo floats. We have demonstrated the possibilities in the recent North Atlantic Bloom (NAB) experiment. Another missing piece is an AUV with the ability go long and slow, like a glider, as well as occasionally go fast when necessary, and be able to navigate in very shallow water (i.e., drive up to the dock). There is no reason why such a propeller driven vehicle cannot have the same endurance as a glider. The third key element is communications, which is also probably in good shape. Argo has demonstrated the great utility of even a very poor communications system (i.e., ARGOS). Iridium is much better and the company appears to have a solid and growing customer base. There appears to be enough global demand for their voice and data services to support this business. The Iridium satellites will need to be replaced before 2025 and the company has been moving forward with plans to do this. There will be many ways to stifle this change with good intentions. We are still in the early stages and the rate of innovation is high. There is a significant danger of freezing the design of a global observing system based on today’s technology, and thus shutting out tomorrow’s technol- ogy. For example, some call for a global system to observe oxygen from Argo floats. This is an excellent idea, but any plans to implement it should not preclude future measurements to observe the carbon system when these sensors become available. We do not yet know how to build an observing system for global ocean biogeochemistry. The ocean’s biogeo- chemical system is very complex, both in the number of variables and in its high degree of spatial and temporal variability. An observing system cannot measure everything, but must measure many things in many places. Figuring out how to do this right is a challenging and important task, with considerable “intellectual merit.” Managing the balance between science and engineering will also be challenging. Ocean science clearly needs good engineering, but keeping the engineering relevant to science requires constant attention. Fortu- nately, the task of designing new sensors, adding them to autonomous

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13 ERIC D’ASARO platforms and using them in creative ways can occur on the scale of a small group of PIs and engineers funded by grants and working with industry. If funding for this type of activity is available, it is easy to imag- ine several groups of this type maintaining a period of “transformational research” in which new ways of sampling the biogeochemical system are developed, tested and, through industrial partners, made available to the broader community. This new technology will change the way that ocean science is con- ducted. Already, the large stream of data freely available on the Internet has allowed many creative and productive physical oceanographers to operate with little direct connection to the process of ocean measurement. This is good for science, since it brings more brains to bear on the impor- tant problems, and good for education, because it allows faculty and stu- dents across the world to participate in research. Oceanography is becom- ing much more like meteorology, with oceanographers distributed more widely across academia, government and industry and with a significant quantity of applied work. As in meteorology, research programs can now be firmly set within a synoptic context defined by the global observing system. We can, for example, study the links between productivity and ocean physics not just “in the Sargasso Sea,” but also at chosen locations within its eddy field. It is inevitable that autonomous platforms will compete with the research fleet. Floats, gliders and moorings now allow us to sample the global ocean in ways that are impossible with ships. Two days of global ship time now cost roughly the same as a glider or 4-6 Argo floats. Today, most biogeochemical measurements are done from ships, thus providing a strong constituency for the maintenance of the fleet. As more and more biogeochemical oceanographers get their data from the web, rather than on cruises, this constituency will decrease. However, ships will always be able to measure more things in more detail than floats or gliders so there is plenty of room for creatively combining the two methodologies. I hope that these new observing technologies will promote interdis- ciplinary research within oceanography and between it and the broader earth systems sciences. Physical oceanography has had remarkable suc- cess by focusing on the dynamics associated with the spatial and temporal variability of the ocean. The new sensors will allow physics and biogeo- chemistry to be sampled on the same space and time scales and thus lead to large advances the understanding their interconnections. Just as the observational tools of physical oceanography applied to geophysical fluid dynamics resulted in today’s observational system, we can hope that the new biogeochemical tools applied to rigorously test and improve today’s primitive biogeochemical models will also result in a system for under- standing and predicting the ocean’s biogeochemistry. Such advances will occur only through the formation of effective interdisciplinary teams spanning the ocean and earth science disciplines.