Where to go?

It’s day 2 of setting up, and since it all came together pretty fast yesterday, today has been a lazy morning. We’ve been lucky enough to be put up in scientist housing provided by the National Park Service, so we’re staying out in Gustavus, around 10 miles away from Bartlett Cove (the parks headquarters). So today we’re going over maps, we’ll meet with the boat captain and we’re going to talk logistics and where we’re going to go.

So how do we choose sites? When you’re searching for corals how do you know where to go? Well first you have to start with a map.

Here’s a map of the central channel of Glacier Bay National Park (check out the “map & timeline” tab at the top to look at a full map) made by Kathy Scanlon & Lane Boyer (USGS). For some of it we have some good multibeam bathymetry (the colored section) which shows us what the bottom looks like underneath all that water. Multibeam bathymetry is made using beams of sound bounced off the bottom and collected on a receiver on the ship, so to collect those maps you not only have to have a boat with the right kind of equipment, but you also have to drive the ship everywhere in the park, so there are still many gaps where we don’t know what the bottom really looks like.

The multibeam maps we have of the park come from Guy Cochrane of USGS, who has been making maps and filling in the gaps, as well as taking camera tows to see what the bottom looks like (black lines). Guy was kind enough to lend us his towed camera video to look at for animals, and every red dot on there is where Kathy Scanlon and I saw corals on the bottom! So naturally, those are the first places we’re going to try and get some pictures of the bottom and take CTD measurements.

So how about areas where we don’t know there are corals or don’t have Guy’s towed camera images, how do we choose the right area to look? Well, it’s not easy, and many times you don’t get it right, but you make the best guess you can based on what you know about cold water corals. We know they like fast currents that bring in food and nutrients, we know they like bottom topography that sticks right out, we know they don’t like lots of sediment (that can suffocate them!) – so here on this map we have chosen A, B, C & D to look for corals. Do you think we’ll find them there? You’ll just have to wait until we’re back to find out!

Now, back to the CTD, the other piece of equipment we’re taking out with us. C (conductivity – measures salinity), T (temperature) and D (depth) is what a CTD measures. Here is a plot Lane Boyer made of some previous temperature data from the middle of the central bay (right outside Bartlett Cove). We can tell a lot from these plots. The blue here is winter (different lines are different years) and the red is summer and the X axis is temperature and the Y axis is depth. This plot tells me that at this location the water is really well mixed in winter – see how the lines are straight up and down. Usually warm water rises and stays at the top forming a layer, and colder water forms layers at the bottom. In the summer you can see this – the sun has heated the water on top making it warmer than that on the bottom, but the water is still well mixed, because usually you’d see a much bigger difference than that. What does this mean? Well, it means it’s probably quite a fast and jumbled current, mixing all the water layers together – just right for cold-water corals!

Here’s another Temperature plot, a bit more confusing – this time this is from right up in the West Arm. This time the blue for winter shows it’s colder on top than on the bottom, probably from ice forming in the top layers making it really cold. In the summer the water on top is much warmer than on the bottom – see the steep lines, in 2009 it was ~7C on top, but 4C down at 300m – that is quite a difference! This plot tells me this area is less well mixed, especially in the summer, so there might be less of a current here, or less of a jumbled current that mixes everything together.

Sometimes it can all be a bit of a puzzle, but we’re starting to collect the pieces. This year remember is just a reconnaissance year, next year we’re hoping to fill in many of the gaps!