Climate Change and the Ross Sea: An Interview with Ocean Scientist, Sharon Stammerjohn

 

 Interview and story by Jordan Cooper

The Ross Sea is a climate anomaly. While temperatures rise throughout much of the continent, accompanied by reductions in sea ice and melting ice shelves, the Ross Sea is actually getting colder.

ImageTo find out how this southernmost region of water is cooling despite a warming planet, I spoke to Sharon Stammerjohn, an ocean scientist at the Institute for Arctic and Alpine Research, who has been studying climate change and sea ice in the Antarctic, for more than 15 years.

We hear a lot about climate change in Antarctica, with ice shelves collapsing and melting, but what is happening in the Ross Sea? 

When we look at regional variability, we primarily see that the Ross Sea is changing really fast towards cooling and sea ice increases, while the area west of the Antarctic Peninsula is also changing really fast but towards warming and sea ice decreases. Elsewhere, the trends are overall weaker. However I would argue that the system is all connected, and that the change in winds (in response to climate change) initiated the sea ice and ocean changes. But why the opposite regional changes? If the Antarctic continent were perfectly circular and symmetric, centered on the South Pole with no peninsula, and showed little topographic relief, then the expectation would be for sea ice increases everywhere (in response to increases in westerly winds). But, because the continent is not centered over the pole, is not perfectly symmetric, has an arm jutting out towards South America and contains considerable topographic relief, this causes strong asymmetries in regional wind patterns, for example, the strong increases in southerly winds in the Ross Sea and strong increases in northerly winds in the Antarctic Peninsula area. Thus, in a somewhat simplified sense, this is how Antarctica’s asymmetric geography responds to the general increase in westerly winds caused by climate change. It imposes strong regional changes between the Antarctic Peninsula and Ross Sea.

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Regional warming and cooling in Antarctica. Photo credit: NASA

Do you anticipate the increasing amount of sea ice in the Ross Sea affecting animals in that region? How?

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A related question is how seasonality is affected. For example, seasonality is affected by the winter duration of sea ice and consequently, the summer duration of open water. That’s what the marine ecosystem really cares about, the timing of autumn sea ice advance and spring sea ice retreat. If you change that – let’s say in the Peninsula area – suddenly your sea ice platform is not there when you need it, for example, for hauling out during spring pupping season or fall molting season, or for accessing fishing grounds. Or, if you suddenly remove the sea ice cover in spring, the lights come back on underwater earlier or at higher latitudes, changing when and where things grow. If the phytoplankton are growing earlier, the zooplankton that feed on the phytoplankton may not be there yet, and then of course there are the predators that feed on the zooplankton. So you get these very strong seasonal mismatches, and not only that, it changes abundances or magnitudes as well. For example, the spring phytoplankton bloom becomes smaller because sea ice is retreating earlier when day length is still short, so growing conditions become less optimal.

The Ross Sea is the opposite story, because there the sea ice is retreating later in spring and advancing earlier in autumn. This may increase spring ice edge blooms but decrease the length of the growing season.

I think basically what happens is that there are winners and losers in the game of climate change. There are some species that can deal with this kind of variability, but it usually results in shifts in species compositions and abundances.

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Do you think the Ross Sea will be a place where animals find refuge as the ice around the rest of the continent begins to melt?

For the Ross Sea marine ecosystem, likely yes, but for species coming from outside the Ross Sea, that will depend on the individual species involved and whether they are capable of migrating or not, or adapting or not. Although the sign of sea ice change is positive in the Ross Sea, the change is still quite rapid. There may be some endemic species not capable of adapting to such rapid change, even positive change.

Is it possible to predict if the trend of increasing sea ice in the Ross Sea is going to continue into the future?

Most predictions suggest that there should be general warming everywhere in Antarctica in the coming century, not just regional warming as currently observed in the Peninsula area. But I wonder if the asymmetry between the Ross Sea and the Peninsula will nonetheless continue to impart regional differences in warming rates. Due to the geography, you’re always going to get some asymmetry in how these two regions respond. So I would guess that the Ross Sea cooling (or slowed warming) may continue into the near future, but into the distant future, I don’t know.

ImageIs it too simple to say that CO2 production by humans is causing increased sea ice extent in the Ross Sea or increasing temperatures in the Western Antarctic Peninsula?

There is a lot of evidence to indicate that this is true. Yes, it’s the increased greenhouse gasses causing changes in the tropics to pole temperature gradient that in turn causes the atmospheric and ocean circulation changes. The fact that the ocean circulation is changing indicates currently observed warming trajectories are not easily reversed.  But to get at the actual mechanisms and feedbacks of these climate-induced changes, we rely on modeling. Unfortunately global climate models do a really poor job in the Southern Ocean. To improve these models, we desperately need more meteorological and ocean measurements.  Antarctica, including the Southern Ocean, is severely under-sampled and data sparse compared to elsewhere on our planet. So we’re not there yet, but we’re getting there, especially with the advent of more robust and autonomous instrument packages. These are increasingly being deployed on the continent and in the surrounding ocean, with real-time data transmission made possible through satellite networks.

Is there anything practical that we can do to reverse these trends that we’re seeing?

I think we have to acknowledge the problem, and I don’t think community-based response should be underestimated. Yes, we need to decrease our CO2 emissions globally, and the US primarily, but are you going to change countries that are developing quite rapidly like China and India that have huge populations? Are you going to stop population growth? That’s not going to happen in the near future, so it’s a really tough nut to crack, and I’m not very optimistic that we will respond in time. It’s characteristic that you really have to be faced with the problem before you can get a region-wide or global response. Image

But I think individuals more and more recognize the problem. I think the message is conveyed better in schools, and I think younger generations are more aware of the interconnectedness of systems and people. Hopefully it’s raising a consciousness that we need to conserve our resources. That’s the bottom line. There are so many ways we can reduce our carbon footprint, but behaviors and expectations will need to change. It’s our biggest challenge because we’re used to everything being at our fingertips. I go to meetings to talk about climate change, and think about the carbon footprint I produce when I do that. It’s huge. We have good intentions, and I think that’s the right way to go. We can do better and we will do better. I think we will be successful in slowing the rate of change, but at this point I don’t think we can reverse it.

 So then the question becomes how do we adapt to change. And I think that’s where the discussion is now. This also relates to the Ross Sea ecosystem, because relative to now, it is the last refuge. Let’s not waste any more time. Let’s focus on it now and learn as much as we can. This is our last chance. It is the last ecosystem on earth relatively untouched by mankind, but, we must act now because there’s no stopping the change.

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