Plastic pollution: an indicator of the Anthropocene?
The contemporary marine environment is undergoing some of the most extreme changes seen for millions of years. Various anthropogenic pressures have led to regional habitat destruction, alteration of food webs, collapse of fish stocks and perhaps more seriously, increased ocean temperatures and acidity affecting biophysical processes and biota on a global scale. There is of course plastic, one of the most recent and novel anthropogenic pressures on the global oceans.
The first reports of plastic litter in the oceans were published in the early 1970s, roughly three-decades after the first commercial manufacturing of plastics in the 1940s and 1950s. At the time, these reports drew minimal attention, however in the 90’s and early 00’s, there were numerous mentions in scientific literature of entanglements/ghost fishing and ingestion of plastics by marine animals.
One of the biggest unknown questions is the long-term fate of plastic in the marine environment. Plastic is incredibly durable and resistant to degradation.
Should plastic waste escape the near-shore environment, it is plausible that these plastics will remain near-intact, particularly if these settle in the dark, cold, deep-ocean. There are no known mechanisms for plastic degradation below the photic zone. In addition, plastic has an estimated longevity of hundreds to thousands of years. If plastics do settle in the dark, cold, deep-ocean, a gradual accumulation of plastic may be observed here.
It is well recognised that human activity has had dramatic and long-lasting impacts on the environment, which led to the suggestion two-decades ago, that we no longer live in the Holocene Epoch and now live in the Anthropocene — the age of man (1).
One of the biggest problems with this, has been to define when the Holocene-Anthropocene transition occurred; a geological time unit requires global-scale changes to be recorded in rocks, glacier ice or marine sediments. It is hypothesised that plastics (particularly microplastics) have the potential to be used as a Global Boundary Stratotype Section and Point (GSSP), which is needed to define a new epoch (2).
Comparisons have been made between plastic and the long-chain polymers found in decay-resistant organic fossils such as wood or spores. Over millions of years these natural items can fossilise from the loss of the material which are expelled as hydrocarbons, leaving an inert, carbon husk and/or impression in the sediment. Using this conceptual framework, we may expect plastic to behave in a similar way on geological timescales (3), thus using plastic fossils as a GSSP for the Anthropocene would seem plausible.
Inspiration from:
(1) Crutzen, P. J. and Stoermer, E. F., 2000. The “Anthropocene”. Global Change Newsletter, 41, 17–18.
(2) Zalasiewicz, J., Waters, C. N., Ivar do Sul, J. A., Corcoran, P. L., Barnosky, A. D., Cearreta, A., Edgeworth, M., Gałuszka, A., Jeandel, C., Leinfelder, R., McNeill, J. R., Steffen, W., Summerhayes, C., Wagreich, M., Williams, M., Wolfe, A. P. and Yonan, Y., 2016. The geological cycle of plastics and their use as a stratigraphic indicator of the Anthropocene. Anthropocene, 13, 4–17.
(3) Zalasiewicz, J., Waters, C. N., Williams, M., Barnosky, A. D., Cearreta, A., Crutzen, P., Ellis, E., Ellis, M. A., Fairchild, I. J., Grinevald, J., Haff, P. K., Hajdas, I., Leinfelder, R., McNeill, J., Odada, E. O., Poirier, C., Richter, D., Steffen, W., Summerhayes, C., Syvitski, J. P. M., Vidas, D., Wagreich, M., Wing, S. L., Wolfe, A. P., An, Z. and Oreskes, N., 2015. When did the Anthropocene begin? A mid-twentieth century boundary level is stratigraphically optimal. Quaternary International, 383, 196–203.
