Paleowave

iMonsoon Climatology

Monthly climatology of precipitation and sea-surface salinity over the Indian Ocean sector.

Monthly climatology of precipitation and sea-surface salinity over the Indian Ocean sector.

Here is a gif (click here for full version) of rainfall over the Indian subcontinent and concurrent sea-surface salinity (SSS) in the Indian Ocean with the targeted sites for Expedition 353 (red circles). The precipitation data are in mm of rainfall per day and the SSS data are displayed in practical salinity units. Each frame displays average monthly data for 55 years from 1958-2013 (i.e. averaging all January data, all February data etc.) There are many things of interest that pop out for me in this animation. Some points of note:

  • The peak of monsoon rain over India is during the months of June, July, and August, or during Northern Hemisphere (boreal) summer.
  • There is a well formed band of rainfall over the southern Indian Ocean during boreal winter.
  • A freshwater pulse (< 30 PSU) close to the eastern coast of India can be observed a month or two after the JJA monsoon peak.
  • During the monsoon, the Bay of Bengal (along with the subcontinent) experiences abundant rainfall.
  • The Arabian Sea is much saltier than the Bay of Bengal.
  • All of the targeted expedition sites display heterogeneity in their seasonality.
  • Many Indian Ocean islands fall prey to poor coastal resolution data (oops!)

What pops out for you? Drop a line in the comments if you'd like details about the methodology.

iMonsoon Playlist

It's been about 15 days since my last blog post and we have already finished drilling five different holes at two different sites, despite downtime. We've seen a lot of core! As I may have mentioned, I'm on the PM-to-AM shift, so I get off my shift at midnight. Though we (lightly) listen to music during our shift, most of my music listening happens off my shift; either in the gym or on the deck (outside). Here's a (mostly complete) list of albums I've been listening to thus far:

  • Mastodon - Once More Round the Sun (most played by far! Which was JUST now promptly deleted thanks to Spotify Offline lasting only for 30 days! #%@&*@#*)
  • Godflesh - A World Lit Only by Fire
  • Yob - Clearing the Path to Ascend
  • Electric Wizard - Time To Die
  • Devin Townsend Band - Accelerated Evolution
  • Aphex Twin - Syro
  • The War on Drugs - Lost in the Dream
  • Crustation - Bloom
  • Bethlehem - Dark Metal
  • Three Mile Pilot - Another Desert, Another Sea
  • Isis - Oceanic
  • Pelican - Australasia
  • The Jesus Lizard - Goat
  • Nick Cave and the Bad Seeds - Let Love In
  • Polvo - Exploded Drawing
  • Nitroseed - Molt
  • Anathema - A Fine Day to Exit
  • Miles Davis - A Kind of Blue
  • Built To Spill - Keep it like a Secret
  • Samael - Passage
  • The Obsessed - Lunar Womb
  • Gorillaz - Plastic Beach
  • Nightingale - I

iMonsoon: Life of a Sedimentologist

The main job of the JOIDES Resolution (or JR for short) is to drill beneath the seafloor and to collect intact sediment cores. Once it gets started, the JR does a really, really efficient job of retrieving core. Every fifteen minutes or so (depending on the water depth at a location, the type of drill bit used, and the characteristics of the material being drilled), one can hear ‘Core on Deck!’ This chant is frequent enough to develop a Pavlov-like reflex.

‘Core flow’ is a JR term to describe the journey of a piece of mud from its inception at the drill rig to its resting place in a U-tube in the basement refrigerator. The scientists at the foremost part of the core flow are those in charge of measuring physical properties on the whole-round core (imagine a clear, plastic cylinder filled with sediments and rocks).

Next, the technicians onboard (who brought out the core from the drill rig via the ‘catwalk’ in the first place) proceed to split the whole-round core into two halves: the working half and the archive half. Many scientists now descend upon the working half, carefully sampling the mud for various chemical and physical measurements. It’s quite a spectacle – especially when we’ve hit a transition or a well-known boundary! What about the archive half? Well, this is where the sedimentologists come into the picture.

The main job of the sedimentologists (8 of us in total on this expedition, with one soon to join) is to describe, characterize, and make detailed reports about the contents of the mud. We are also responsible for walking the archive halves through the SHIL and SHMSL: two fancy imaging instruments that can take high-resolution photographs, and make color-based and magnetic susceptibility measurements which become important for the stratigraphic correlators onboard.

Once these scans are finished, the fun begins. Using tried and tested, yet basic, tools (see picture) we try and characterize the makeup of the mud. We document the colors using Munsell charts, note the texture of the sediments using the spatula, and then try and see interesting features using our hand-lens. It is also our job to document how the drilling process might have disturbed the recovered cores. Another vital aspect of the description process is making smear slides, where a small amount of sediment is taken on a glass slide for observation under a powerful microscope. This can be really handy for distinguishing the amounts of clay, silt, sand, and even identifying minerals or volcanic ash!

After the first five cores or so, all of us sedimentologists (4 in the day shift) became cogs of a bigger, well-oiled machine. Mind you, there were ~50 cores in the first hole, each composed of 4-7 1.5 m sections (!) – so we see a LOT of core, and during most parts, it can be run-of-the-mill. However, when something exciting does pop up (which can happen quite frequently at times), we usually all gather around the description table, huddle together, take notes and photographs, and have lively conversations and debates, and ultimately marvel at how we can catch glimpses of a world that was millions of years younger…