Science Response 2012/006

Transport of marine debris from the 2011 Tōhoku tsunami to the west coast of Canada

Context

On December 9, 2011, Fisheries and Oceans Canada’s (DFO) Ocean Sciences Division (OSD) in Pacific Region requested that DFO Science, Pacific Region, provide information and advice regarding the transport of debris to the west coast of Canada from the March 2011 earthquake and tsunami in Japan. This request arose because the OSD has received multiple requests from other federal government departments and agencies, the Province of British Columbia, and the media for information on the timing, location and quantity of debris generated by the earthquake and tsunami that might reach Canadian waters and shorelines. The OSD requested responses to the following:

  1. When and where is debris from the 2011 Tōhoku tsunami expected to reach Canadian waters and shorelines?
  2. What types of material are expected in the debris and what is the estimated quantity of material likely to enter Canadian waters and/or reach shorelines?
  3. What monitoring of the debris is occurring while it drifts at sea from a Canadian/international perspective?
  4. What risks, if any, does this debris pose for species, habitats, and ecosystems in Canadian waters? and,
  5. What are the potential navigational impacts in Canadian waters?

This Science Special Response Process (SSRP) was based on existing information on the debris and two independent ocean circulation models of simulating debris movements and drift rates in the North Pacific Ocean, both of which are subject to considerable uncertainty due to the minimal observation and tracking of debris, the diffuse nature of the debris field, and the absence of formal testing of the models. A SSRP was used because DFO Science was asked only to review the information available on the issue rather than data collection methods or the simulation models and their results.

The responses/conclusions of the SSRP are:

  1. When and where is debris from the 2011 Tōhoku tsunami expected to reach Canadian waters and shorelines?   Based on model forecasts, debris from the March 2011 tsunami is expected to begin arriving in waters off North America in 2013 and will likely continue to arrive over a large spatial area from Alaska to California for several years.   * However, high windage objects may be driven by the prevailing westerly winds and move more quickly towards the North American coast than the surface waters that are likely transporting most of the debris. Thus, high windage objects may begin arriving along the coast of British Columbia earlier than the bulk of the debris, which is forecasted to begin arriving in the first half of 2013. Most of this debris will consist of small pieces rather than large objects or debris fields owing to the effects of surface currents, winds, and waves.  It is important to note that the debris generated by the tsunami will be an addition to the existing debris load floating into Canadian waters and washing ashore in British Columbia every day.  Existing patterns of debris deposition on shorelines are not expected to change when debris from the tsunami begins arriving.  Since the origin of the most debris washing ashore is not identifiable, the only indicator of tsunami debris may be an increase in the quantity of debris (by weight) washing ashore relative to the long-term average.  It is unlikely that debris from the tsunami will enter the Strait of Georgia due to surface water properties and currents at the mouth of the Strait of Juan de Fuca.
  2. What types of material are expected in the debris and what is the estimated quantity of material likely to enter Canadian waters and/or reach shorelines?  Both the quantity and composition of tsunami debris expected to reach North America are highly uncertain.  Initial estimates of the mass of debris swept into the ocean ranged between 20 and 25 million tonnes.  However, an updated estimate from the Government of Japan is that 1.54 million tonnes of tsunami-generated debris remains afloat as of March 2012.  Independent confirmation of these figures is lacking at present and the composition of the debris is poorly known.  Based on existing knowledge of oceanographic processes and marine debris transport, only the most buoyant and durable objects will survive the trans-Pacific crossing and reach North America.  Models used to forecast debris movements show that most of the tsunami debris will remain in the ocean for many years and collect in the North Pacific Garbage Patch. It is unlikely that debris caught in the Garbage Patch will subsequently reach the coast of British Columbia.
  3. What monitoring of the debris is occurring while it drifts at sea from a Canadian/international perspective?  Debris swept into the Pacific Ocean was tracked by satellite for about one month after the tsunami.  An attempt to locate debris with high resolution satellite imagery in December 2011 was unsuccessful.  In the absence of systematic monitoring of debris by satellites, opportunistic sightings by passing vessels have been compiled and catalogued by the Government of Japan.  Shoreline monitoring to collect baseline data on the quantity and composition of marine debris washing ashore in Washington is occurring and may expand to Oregon and California. At present, there is no formal systematic shoreline monitoring program in British Columbia, although some baseline data may be available from annual beach clean-up days coordinated by environmental non-governmental organizations.
  4. What risks, if any, does this debris pose for species, habitats, and ecosystems in Canadian waters?  It is impossible to quantify the risk to marine species, habitats or ecosystems in British Columbia associated with tsunami debris and whether this risk surpasses any thresholds for effects.  The baseline risks to marine habitats, species and ecosystems in Canadian waters from the existing marine debris load are poorly understood and documented and as a result the expected incremental increase in risks associated with the arrival of tsunami debris cannot be estimated at present.  However, the risks from radioactivity on the debris associated with 131I and 137Cs originating from the Fukushima nuclear plant are believed to be low.  Limited testing of tsunami debris collected by a Russian research vessel in September 2011 found that radioactivity levels were below detection limits.
  5. What are the potential navigational impacts in Canadian waters?  Navigational impacts in Canadian waters associated with marine debris are poorly known.  The highest risk to navigation is likely related to large objects (e.g., shipping containers, houses, etc.) arriving in coastal waters, but the probability of these objects surviving a trans-Pacific crossing intact is believed to be low.  Although drifting nets, ropes and other entangling debris from the tsunami pose a risk, this risk and the resulting impacts are likely incremental increases on the current navigational risks associated with entangling debris.  Small objects (e.g., logs or small pieces of wood) are not believed to pose any additional risk to vessel traffic off the west coast of Vancouver Island.  Tsunami debris, when it arrives, is unlikely to pose a risk to vessel traffic in the Straits of Juan de Fuca or Georgia since water properties and current patterns will inhibit the movement of debris into these water bodies.

Although some of the debris from the 2011 Japanese tsunami will eventually reach North America, there remains considerable uncertainty with respect to the quantity and composition of debris still floating, the location of the debris, the pathway of the debris, and the timing and quantity of debris that will arrive.  To address these uncertainties, recommendations to update this advice as new information becomes available from other Government agencies and to coordinate monitoring and surveillance are provided.

This Science Response report is from the Fisheries and Oceans Canada, Canadian Science Advisory Secretariat, Regional Science Special Response Process (SSRP) of March 6, 2012 on the Transport of Marine Debris from the 2011 Tōhoku Tsunami to the west coast of Canada.

 *  Updated: June 2012

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