Ensuring healthy marine ecosystems and sustainable harvest of living marine resources are of considerable economic, social and cultural significance [Reimer et al., 2015]. Dramatic changes have already occurred in higher trophic levels of the marine food web due to anthropogenic influences, primarily overfishing [Worm and Branch, 2012]. Other anthropogenic environmental stressors influence marine ecosystems including rising temperatures and acidity and decreasing oxygen availability ([Pinsky et al., 2013]; [Doney et al., 2012]). The effects of these changes will manifest themselves more drastically over the coming century. The need to anticipate and mitigate the potentially dramatic effects of the rapidly changing marine environment on ecosystems and marine resources is urgent and is increasingly recognized [FAO, 2013; 2014]. For example, legislation mandating ecosystem-based approaches for the management of living marine resources in Europe [EU, 2014] and in Canada [Oceans Act, 1996], and recently announced increases in Marine Protected Area in the US [White House, 2014] are reflections of a growing recognition that marine ecosystems and their resources are threatened and along with a willingness to take action.
Longer term oceanic changes over interannual (e.g. ENSO) to decadal and climatic time frames tend to be manifested as shifts in the timing of seasonal and sub-seasonal processes. Such phenological changes can lead to mismatches in ecosystem coupling. For example, vertical migrating zooplankton may be missing the spring phytoplankton bloom that is their key food source. Resolving this coupling across scales cannot be achieved except through sustained high-frequency observing of the interior ocean biogeochemistry. Understanding these coupling modes will provide insights needed to assess ecosystem tipping points ahead of full-scale regime shifts, such as have been associated with the collapse of some major fisheries.
The Biogeochemical-Argo network would provide an important underpinning for the observation of changes occurring at the base of the food web, for the attribution of changes in higher trophic levels to environmental stressors, and for the development of predictive capabilities for marine living resources. The network would, for the first time, enable monitoring, on a global scale, for environmental conditions such as acidity (pH) and oxygen concentrations, which directly affect physiological functions and fitness of various important species, and nitrate concentrations and plankton biomass, which determine productivity at the base of the marine food web. Observations of variability and trends of these properties are necessary for proper attribution of changes at higher trophic levels to environmental conditions. The Biogeochemical-Argo observations would also provide much needed information to constrain, validate and improve lower trophic level models – improvements in realism of these models has been severely hampered thus far by a lack of global, depth-resolved biological and chemical observations. Such models can interface between the ocean’s biochemical environment and higher trophic levels [Bianucci et al., 2016].