In a somewhat unexpected turn of events, earlier this week I attended a lecture discussing ocean warming in the Tasman Sea. It is not at all unexpected that I would attend a lecture so relevant to my PhD, it was more the crowd and location that were a break from the norm. The ‘Friends of the Botanical Gardens’ invited Dr Wenju Cai from the CSIRO to give this week’s seminar; following last weeks talk ‘Illuminated: an illuminating presentation of Solomon’s Song of Songs, Ruth, Lamentations, Ecclesiastes and Esther from the Bible’, and leading next week seminar focusing on ‘Pruning Australian Native Plants’. However, due to the relevance of the talk I cast any reservations aside and joined Canberra’s retirees in the garden’s theaterette. Dr Cai delivered an excellent talk to the sea of top knots and cable-knit cardigans, engaging and informing the unlikely crowd about his latest ocean-atmosphere coupled climate models.
The ocean is warming as most have probably heard, however what might be news is that there are specific regions known as ocean hotspots, where temperatures are accelerating beyond expectation. Oceanographers have identified many such temperature anomalies that are generated by strengthening wind systems that drive oceanic currents polewards beyond their known boundaries; including the Aghulhas current off the African coast, the Kurioshio current near Japan, the Gulf Stream and our own East Australian Current, . Motivated by previous observations of warming in the Tasman Sea, the new research took a global perspective and found a synchronised, enhanced warming signal. Both the hole in the ozone layer, as well as accelerating atmospheric CO2 concentrations, were implicated in altering the wind stress curl (or gradient in wind strength) over the ocean. This causes circulation in certain regions to ‘spin up’ and bring warmer waters further south, with consequences for marine biodiversity and invasive species, aswell as the ocean’s ability to act as a heat and carbon sink. Other evidence includes a poleward shift of weather systems and expansion of the tropics, that will affect regional rainfall. He demonstrated this by showing the weather system that produces rainfall over Perth. Their unrelenting drought is due to the rainfall occurring, ever increasingly, further south over the ocean, which they can still drink, once it’s been through the city’s desalination plant.
I’m not entirely sure my grandmother would have followed every slide -she died 20 years ago so she definitely wouldn’t follow any slide now. But even with life on her side there were certain parts of the talk that may have been difficult for her to follow. But I did! Actually it was an excellent synthesis of some rather complex systems, and it pulled together many pieces of the puzzle I hadn’t quite put together myself. I wonder if I can get the “friends” to hold a seminar on compound specific nitrogen isotopes in deep-sea coral……