Impact of remotely generated eddies on plume dispersion at abyssal mining sites in the Pacific

Abstract

Proposed harvesting of polymetallic nodules in the Central Tropical Pacific will generate plumes of suspended sediment which are anticipated to be ecologically harmful. While the deep sea is low in energy, it also can be highly turbulent, since the vertical density gradient which suppresses turbulence is weak. The ability to predict the impact of deep plumes is limited by scarcity of in-situ observations. Our observations show that the low-energy environment more than four kilometres below the surface ultimately becomes an order of magnitude more energetic for periods of weeks in response to the passage of mesoscale eddies. The source of these eddies is remote in time and space, here identified as the Central American Gap Winds. Abyssal current variability is controlled by comparable contributions from tides, surface winds and passing eddies. During eddy-induced elevated flow periods mining-related plumes, potentially supplemented by natural sediment resuspension, are expected to spread and disperse more widely and rapidly. Predictions are given of the timing, location and scales of impact.

Implications of population connectivity studies for the design of marine protected areas in the deep sea: An example of a demosponge from the Clarion‐Clipperton Zone

“…Modelled currents at the 3,500 m level used for advective dispersal simulations are strongly bathymetrically constrained, so mean flow patterns (Figure ) showed considerable spatial complexity. Superimposed on these mean patterns is variability induced in part by the deep penetration of passing eddies and other flow structures higher in the water column (Aleynik et al., ). The dispersal of simulated particles therefore reflects intricate stirring with a weak underlying tendency towards a net movement to the north and east (Figure a–e; Supporting information ).…”

“…Superimposed on these mean patterns is variability induced in part by the deep penetration of passing eddies and other flow structures higher in the water column (Aleynik et al, 2017). The dispersal of simulated particles therefore reflects intricate stirring with a weak underlying tendency towards a net movement to the north and east (Figure 6a-e; Supporting information Video S1).…”

“…In the absence of detailed understanding of larval behaviour and vertical positioning, transport was simulated within the horizontal model layer at 3,500 m depth, representing the lower water column at a level that is largely unobstructed by topography. Modelled currents at this depth are weak (the mean instantaneous current speed in a box encompassing the sample sites is 2.2 cm/s, and the mean residual flow speed, the mean of the underlying mean flow, is 0.5 cm/s; Aleynik, Inall, Dale, & Vink, ). Larval connectivity between sites X and Y (the four different areas in our study) was assessed by continuously releasing “particles” (1,000 per day) from site X throughout the first 4 years of the record, and determining the probability that they pass within a 25 km radius of site Y at any time within the following 5 years.…”

Ecology of a polymetallic nodule occurrence gradient: Implications for deep‐sea mining

“…Although these may act as source populations of taxa that do preferentially occur in high nodule abundance areas (i.e., Anthozoa or Bryozoa), our results suggest that they cannot support the abundant populations of these taxa found in high nodule cover areas (i.e., Isididae corals). Moreover, the potential deposition of sediment plumes in nondirectly exploited areas (Aleynik et al ; Peukert et al ) may also compromise the preservation of source populations for most suspension feeder taxa (Bluhm ). The latter represent the vast majority of the metazoan standing stock in the CCZ (Amon et al ; Vanreusel et al ) and appear to be the most sensitive to variations in nodule cover (i.e., this study).…”

“…This unusual and diverse habitat is potentially subject to imminent large‐scale human impacts in the form of seafloor mining (Wedding et al ; Kuhn et al ). Mining disturbances are likely to extend over extremely large seafloor areas (Aleynik et al ) and have a clear potential to drive major changes in the resident fauna (Jones et al ). Predicting the nature of such changes remains difficult; the ecology of this remote habitat is poorly understood, in particular, very little is known of the biodiversity associated with nodules (Veillette et al ; Vanreusel et al ).…”