|
Prajakta Niphadkar, who is working on an MSc project on sea level around New Zealand, visited Xuebin Zhang at CSIRO, Hobart, in July. I had the fantastic opportunity in July to fly down to Hobart, a beautiful coastal city nestled beneath Mt Wellington in Tasmania. I spent my week in Hobart at CSIRO Oceans and Atmosphere with sea level scientist, Xuebin Zhang. Xuebin provided me with valuable guidance and some great insights on sea level variability. We worked with scientists from various areas of expertise to address some challenging aspects of New Zealand’s coastal sea level, such as the complexity of vertical land motion around the country. Xuebin also shared insights on his recent work on high-resolution, regionally-downscaled future sea level projections. My visit to Hobart made for a great learning experience and a valuable contribution to my sea level study. I hope to be back again soon! (Pictured: CSIRO’s RSV Investigator ship, docked and ready to host visitors for the Australian Antarctic Festival weekend.)  Several fast, narrow boundary currents flow along the eastern margin of New Zealand forming part of the western boundary current system of the South Pacific. The currents play a critical role for the physical and biological environment because the transport of heat, salt and nutrients influences the regional climate and biota including fisheries off the east coast of New Zealand. Our study shows that, individually, the currents have their own intrinsic variabilities and show considerable interannual variation. There is no evidence of trends in the transport of the currents and there is little correlation with each other and with winds. This is the first comprehensive description of the variability and forcing mechanisms of the New Zealand boundary currents studied simultaneously. A research article was recently published in Progress in Oceanography: Article: “Fernandez, D., Bowen, M., and Sutton, P. (2018), Variability, coherence and forcing mechanisms in the New Zealand ocean boundary currents, Prog. in Ocean., 165, pp. 168-188. https://doi.org/10.1016/j.pocean.2018.06.002 ”   The latest from Aitana --
After a few days of almost perfect weather, with flat sea and almost no wind, finally the “screaming sixties” are showing up.The sea looks like a washing machine, waves coming from any direction, chaotic, without order, and enormous, a lost iceberg makes its appearance in the fog. There is almost no wind, I think we are in the middle of two weather systems, one to the north, one to the south. The officer on shift confirms that we have an 8-9 swell from the northwest, and another one building up from the south of 5-6 meters. All the operations are postponed and we are making our way further north where waves are a bit smaller, we still have 15 hours of “washing machine” transit. The only option is to wait until this is over. After all, we are in the Southern Ocean, there is no place to hide.  The latest from Aitana --
Today we have deployed the last of our long term instruments called “moorings”. A mooring is a line of rope anchored to the ocean floor (with train wheels). Along this rope there are different instruments that measure different variables depending on what processes we want to capture. For example, we can measure temperature, salinity and currents at different depths. The moorings will stay in the ocean recording data for 11 months until next year when they will be picked up. One of the interesting things about the moorings is that, because they are recording data over the year, they can capture processes that occur in the winter, when it is impossible to come here to sample. On the other hand, we need the ice conditions to be the same as this year (no ice at all!) to be able to recover them next year! The sea conditions for this deployment were fantastic, flat sea and almost dead calm, although we had some heavy snow to make everything more beautiful!  On the way to the Ross Sea the scientists went through many safety drills. Here's three of them practicing getting into survival suits -- Aitana Forcen Vazquez (right) from MetOcean, our lead physical oceanographer, with Moira Decima and Sadie Mills of NIWA.
Here is the first profile of temperature (black line on left plot) and salinity (black line on right plot) from one of the Argo floats deployed at 64˚S, 171˚E north of Cape Adare, in the Antarctic Circumpolar Current region. The green curve in the profiles represent the mean climatological values for temperature and salinity respectively for that location. We can observe that the water is warmer than the climatological mean in the first 100 m and below 200 m, it looks like Summer time! The difference between the mean salinity and the recent measured one is much smaller. Let’s see how these profiles change in a few cycles after the Argo float drifts with this powerful current.  Measuring the Southern Ocean...  The CTD measures conductivity, temperature and depth. It is a central instrument for measuring the properties of ocean water. The instrument is in the centre of the frame and is surrounded by bottles (the grey cylinders in the photo). The frame is lowered by cable over the side of the ship. As it is lowered towards the bottom, the CTD returns a profile of the water properties.
The first CTD cast has been completed on Tangaroa -- a deep one -- over 5000m.  Today is our fifth day at sea. We have been very lucky with the weather so far as the sea has been very calm for Southern Ocean standards. A gentle swell has been easing our way into the vessel life. Drills, meetings and planning are keeping us busy since we left Wellington on a beautiful sunny day. Since yesterday, we have been deploying Argo floats and drifter buoys.
The Argo floats they drift with currents, for 10 days, at a parking depth of 1000 m. After drifting at depth for 10 days the floats sink to another 1000 m and then re-emerge to the surface while measuring temperature and salinity (so temperature and salinity profiles are 2000 m 'long'). At the surface they transmit the data to a satellite and the floats submerge again to the 1000 m parking depth. This cycle is repeated every 10 days. Drifter buoys measure the height and period of waves. Some of the drifter buoys only measure temperature at the sea surface and the surface pressure. Today, we have finally deployed the first CTD (conductivity, temperature and depth), a first profile of 5300 metres depth! We took samples for oxygen and salinity, the coldest water so far was at 5000m, 4 degrees Celsius. Tomorrow we are crossing 60S, exciting!  Aitana has sent us this picture of Tangaroa leaving Wellington bound for the Ross Sea!
 Tangaroa leaves Wellington next week to measure the deep outflow of the Ross Sea. The physical oceanography team on board will be Aitana Forcen-Vazquez (MetOcean), Matt Walkington (NIWA) and Sarah Searson (NIWA). Aitana will be sending posts from sea so you can follow the voyage here.
Funding is from the Deep South National Science Challenge ("Taking the Pulse of the Ross Sea Outflow"). (Photo credit: NIWA) |
AuthorMelissa Bowen is a Senior Lecturer in the School of Environment at the University of Auckland Archives
September 2018
Categories |
RSS Feed