Cruise Day 33
Speed 0 knots (kts) Course 152° (SSE) Location Lomonosov Ridge Depth 2749 m
GO DEEPER DISCUSSION: (see previous journal for the questions.)
Sun dogs (also known as parhelia), are created by hexagonal ice crystals in clouds refracting sunlight. They act like zillions of little prisms, spreading light into a spectrum at an angle of about 22° from the sun. Sun dogs are usually seen when the sun is low in the sky due to the way that slowly settling ice crystals in clouds orient themselves to the ground. (If the ice crystals are randomly oriented, a full ring around the sun called a 22° halo can be observed higher in the sky.) Clouds made of ice crystals are common in the Arctic year-round, and the sun stays low in the sky, so conditions to see this phenomenon are often present up here when the sun is above the horizon. In temperate regions, clouds with suitably-formed ice crystals usually occur in the winter, and the sun is also lower in the sky then. So if you live in the lower 48 states, keep an eye out this winter for sun dogs! (But remember, never look directly at the sun.)
A Northern Fulmar coursed over the open lead where we were conducting water sampling operations yesterday evening just 130 nautical miles south of the North Pole.
TODAY’S JOURNAL:
We are settled in on a full sampling station that began yesterday afternoon. For almost two days now we’ve had southerly winds and snow. Despite our mild temperature (31° F today, the warmest we’ve seen for weeks) it feels pretty raw to be out on an exposed part of the deck. Luckily, the Mustang suits that we wear for work safety shed the weather pretty well. That, along with physical activity, kept me warm when I went out twice last night to help with the GEOTRACES deep water cast. Yesterday evening I was very pleased to see a Northern Fulmar, the first bird I’ve seen since August 22. This is the longest I think I’ve ever gone without seeing some kind of bird, and by far broke my personal record for the most northerly sighting (which previously was a Black-legged Kittiwake around 78.8° N.) A ringed seal also appeared in the lead that we’re stopped in for water sampling, but will fall short of the most northerly animal of any kind I’ve seen because of the Bearded Seal that we saw one mile south of the North Pole a few days ago.
Yesterday I outlined the protocol for sampling clean ice, snow, and sub-ice seawater. It turns out that scientists are also very interested in dirty ice, and as we transit between ice stations, a lookout is kept for chances to sample it. Dirty ice is kind of just what it sounds like – ice with a bunch of muddy sediment in it. The dirty ice is easy to spot unless lots of snow is covering it – among the backdrop of pastel blues and white there will be obviously contrasting earthy browns added to the palette. This is most easily seen when we break through dirty ice, scattering it in our watery wake, or if some gets pushed up in a pressure ridge.
A piece of dirty ice in our wake contrasts with the blues and whites of clean sea ice.
Dirty ice in this pressure ridge is also conspicuous despite fresh snow cover on its surface.
Dirty ice is formed when storms churn up shallow water on the continental shelf. If this happens in the fall, temperatures can drop low enough for sea ice to begin to form, trapping the sediment from the muddy water in the ice. Dirty ice can also form next to shore when ice freezes all of the way to the bottom, picking up bottom sediment in the process. As the ice thaws some and breaks up in the spring, winds and currents can get it moving out away from shore, taking its cargo of sediment with it. In Arctic river deltas, sometimes ice dams form during spring runoff causing the rivers to carry sediment-laden water out onto the surface of the ice. Again, this can re-freeze into dirty ice and be carried out to sea.
Once dirty ice gets offshore, winds and currents can carry it long distances, potentially thousands of kilometers away from its source. Scientists have sampled and characterized the sediments in major Arctic river deltas and in many continental shelf areas around the Arctic Ocean. Each area has what amounts to a sediment signature, so if dirty ice can be recovered and the sediments extracted by melting and filtering, the origin of the ice can be narrowed down to a specific region. This gives clues to Arctic ice movement. In addition to where the ice came from, short-lived radioactive isotopes such as polonium in the sediments can be used as timers to hint at when the dirty ice formed. As the ice eventually melts and releases its load of sediment, it is also a major source of trace metals into the otherwise quite clean, clear deep Arctic basins. So dirty ice is much desired by several groups of scientists aboard on this cruise and at labs off the ship.
A couple of days ago, a tall pressure ridge was spotted that looked nicely dirty. The Healy stopped alongside the ridge and lowered Tim Kenna (Research Scientist at the Lamont-Doherty Earth Observatory at Columbia University) and Dan Gomes (Bosun’s Mate, 3rd Class) onto a floe via a so-called man cage suspended from a crane. They walked over to the pressure ridge and sampled the dirtiest ice they could find with picks and a hatchet. The ice was returned to the ship in buckets and bagged up to be melted for analysis.
A man basket (hey, women can use it too…) is lowered onto the ice by a crane for a dirty ice sampling operation yesterday evening.
Tim Kenna and Dan Gomes going after dirty ice in a pressure ridge in the Arctic Ocean.
Tim Kenna sampling dirty ice from a pressure ridge in the Arctic Ocean.
GO DEEPER!
Some pieces of ice we see are mostly clear blue but with a brown layer through the middle. Can you think of a scenario that could create ice like this?
Aloft Con web cam updated every hour
Healy Track
That's all for now. Best- Bill