If model parameterizations of unresolved physics, such as the variety of upper ocean mixing processes, are to hold over the large range of time and space scales of importance to climate, they must be strongly physically based. Observations, theories, and models of oceanic vertical mixing are surveyed. Two distinct regimes are identified: ocean mixing in the boundary layer near the surface under a variety of surface forcing conditions (stabilizing, destabilizing, and wind driven), and mixing in the ocean interior due to internal waves, shear instability, and double diffusion (arising from the different molecular diffusion rates of heat and salt). Mixing schemes commonly applied to the upper ocean are shown not to contain some potentially important boundary layer physics. Therefore a new parameterization of oceanic boundary layer mixing is developed to accommodate some of this physics. It includes a scheme for determining the boundary layer depth h, where the turbulent contribution to the vertical shear of a bulk Richardson number is parameterized. Expressions for diffusivity and nonlocal transport throughout the boundary layer are given. The diffusivity is formulated to agree with similarity theory of turbulence in the surface layer and is subject to the conditions that both it and its vertical gradient match the interior values at h. This nonlocal “K profile parameterization” (KPP) is then verified and compared to alternatives, including its atmospheric counterparts. Its most important feature is shown to be the capability of the boundary layer to penetrate well into a stable thermocline in both convective and wind-driven situations. The diffusivities of the aforementioned three interior mixing processes are modeled as constants, functions of a gradient Richardson number (a measure of the relative importance of stratification to destabilizing shear), and functions of the double-diffusion density ratio, Rρ. Oceanic simulations of convective penetration, wind deepening, and diurnal cycling are used to determine appropriate values for various model parameters as weak functions of vertical resolution. Annual cycle simulations at ocean weather station Papa for 1961 and 1969–1974 are used to test the complete suite of parameterizations. Model and observed temperatures at all depths are shown to agree very well into September, after which systematic advective cooling in the ocean produces expected differences. It is argued that this cooling and a steady salt advection into the model are needed to balance the net annual surface heating and freshwater input. With these advections, good multiyear simulations of temperature and salinity can be achieved. These results and KPP simulations of the diurnal cycle at the Long-Term Upper Ocean Study (LOTUS) site are compared with the results of other models. It is demonstrated that the KPP model exchanges properties between the mixed layer and thermocline in a manner consistent with observations, and at least as well or better than alternatives.

Oceanic vertical mixing: a review and a model with a nonlocal boundary layer parameterization

As part of the activities of the Global Ecology and Oceanography of Harmful Algal Blooms (GEOHAB)programme, Open Science Meetings (OSMs) have been organized to discuss and synthesize research efforts on various aspects of harmful algal blooms (HABs), and to plan future collaborative activities relevant to the research
theme. Within this framework, the steering committee of the GEOHAB Core Research Project on HABs in Fjords
and Coastal Embayments has organized two OSMs. The first OSM was held in 2004 in Santiago, Chile;
the major goals were to identify the primary research priorities and to initiate an agenda to further our understanding of HAB dynamics in these small-scale coastal systems. The second OSM was held in May 2012 in Victoria,Canada to highlight the progress accomplished since the first OSM and to focus attention on the importance of a comparative approach in conducting ecosystem studies to improve our understanding of HABs. This second OSM addressed four major themes for which significant advances have been made in recent years,
with particular focus on their application to semi-enclosed basins linked to coastal ecosystems: (1) Life
history of HAB species; (2) Chemical ecological and toxin interactions; (3) Genetic diversity and (4) Transport and mixing of blooms in small-scale, mesoscale and semi-confined systems.

This Report presents the major outcomes of this OSM, followed by recommendations for future collaborative
studies. These recommendations include the maintenance of international activities on the ecology and oceanography of HABs after the end of the GEOHAB programme in December 2013. A future agenda
should focus on a few key questions with clearly identifiable deliverables. These questions should include
the development of (i) improved methods to determine the rates of cyst formation and germination in the field,
and (ii) coupled biological-physical-chemical models more appropriate to small-scale environments and
which incorporate the role of allelochemicals and toxins, as well as the pelagic and benthic coupling components. Research devoted to life history stages should be continued, particularly with respect to fish-killing algal species that cause particular damage in coastal environments. The influence of aquaculture activities on the development of HABs is poorly understood and should be of greater concern in future research on HABs. The influence of climate change, which may be exacerbated
in coastal environments, also should be a focus of future research. Long-term ecological research should be
encouraged in this respect, in order to make better predictions in the future concerning the development of
HABs in coastal environments.

Global Ecology and Oceanography of Harmful Algal Blooms, GEOHAB Core Research Project: HABs in Fjords and Coastal Embayments. Second Open Science Meeting. Progress in Interpreting Life History and Growth Dynamics of Harmful Algal Blooms in Fjords and Coastal Environments.

Surface sediment dinoflagellate cysts from the Hudson Bay system and their relation to freshwater and nutrient cycling

Among the organisms that spread into and flourish in Arctic waters with rising temperatures and sea ice loss are toxic algae, a group of harmful algal bloom species that produce potent biotoxins. Alexandrium catenella, a cyst-forming dinoflagellate that causes paralytic shellfish poisoning worldwide, has been a significant threat to human health in southeastern Alaska for centuries. It is known to be transported into Arctic regions in waters transiting northward through the Bering Strait, yet there is little recognition of this organism as a human health concern north of the Strait. Here, we describe an exceptionally large A. catenella benthic cyst bed and hydrographic conditions across the Chukchi Sea that support germination and development of recurrent, locally originating and self-seeding blooms. Two prominent cyst accumulation zones result from deposition promoted by weak circulation. Cyst concentrations are among the highest reported globally for this species, and the cyst bed is at least 6× larger in area than any other. These extraordinary accumulations are attributed to repeated inputs from advected southern blooms and to localized cyst formation and deposition. Over the past two decades, warming has likely increased the magnitude of the germination flux twofold and advanced the timing of cell inoculation into the euphotic zone by 20 d. Conditions are also now favorable for bloom development in surface waters. The region is poised to support annually recurrent A. catenella blooms that are massive in scale, posing a significant and worrisome threat to public and ecosystem health in Alaskan Arctic communities where economies are subsistence based.

Evidence for massive and recurrent toxic blooms of Alexandrium catenella in the Alaskan Arctic

Abundance and distribution of toxic Alexandrium tamarense resting cysts in the sediments of the Chukchi Sea and the eastern Bering Sea

Trophic cascades and future harmful algal blooms within ice-free Arctic Seas north of Bering Strait: A simulation analysis

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Trophic cascades and future harmful algal blooms within ice-free Arctic Seas north of Bering Strait: A simulation analysis