Understanding Early Diagenesis: A Two-Part Story

By Catherine Drake, Invertebrate Zoology Lab

Part One

Sedimentation is the process by which particles sink and accumulate on the seafloor. Layers upon layers of these settled materials tell the story of the oceans and climate from which they originated. Alterations to these sediments from compaction, bioturbation, and microbial respiration form sedimentary rocks through an action termed diagenesis.  A better comprehension of diagenesis is needed to translate the sedimentary record into clues that help explain past events. To better understand these processes, students at MLML take the MS 274 “Advanced Topics in Oceanography” course.  This class, taught by Dr. Ivano Aiello and Dr. Kenneth Coale, examines the factors that affect sedimentation and subsequent diagenesis in Monterey Bay.

A major driver of sedimentation is the ocean “biological pump.” This is the fixation of carbon by phytoplankton and the subsequent transport of plankton debris to depth.  Over time, these sediments undergo diagenesis as more sediments are deposited and compacted or consumed and disturbed by organisms. The process of diagenesis mimics many of the same processes as we observe in a compost pile, but occurs much slower.

The ocean biological pump. (Source: http://www.nature.com/nature/journal/v407/n6805/full/407685a0.html)

To study which organisms drive the biological pump in Monterey Bay, the MS 274 class constructed sediment traps. To build the array, we first mastered the technique of splicing rope together, which held our sediment traps to a mooring approximately 30 feet from the seafloor.  Then, we attached a subsurface float that held eight replicate sediment traps just above the sediments.  On top of the array, we fastened a surface float to aid in recovery.  The purpose of the array was to catch fresh material that we could compare to materials in the sediments.

Emily Donham and Catherine Drake learning to splice rope to use for our sediment trap array. Photo by: Diane Wyse

Dr. Kenneth Coale drew a schematic for our sediment array. Photo by: Diane Wyse

On September 24, 2012, we boarded the R/V John H. Martin and set a course for a location in Monterey Bay that was approximately 60 feet deep and deployed our sediment trap array.  The traps were left for two weeks before they were retrieved on October 8, 2012.  In addition, we collected sediment cores from the trap location from the R/V Point Sur in order to retrieve older material from comparison.

Once in the lab, we conducted scanning electron microscopy (SEM), elemental analysis and petrographic microscopy to characterize both fresh and deposited materials.  Stay tuned for part two, where we present and interpret our findings!

The MS 274 class waits aboard the R/V John H. Martin to reach the sediment trap deployment site. Photo by: Catherine Drake

And Now for Something Completely Different

by Angela Szesciorka, Vertebrate Ecology Lab

Most of my posts tend to reflect my love of marine mammals, specifically the large, “charismatic whales” as they are oft referred to.

But I wanted to tell you about one of my day jobs. [As if grad students have all this time in-between taking classes and working on their thesis. But I digress … ]

I work for a marine engineering company in Santa Cruz, doing coastal engineering. Or, what we tell the general public: we play with mud.

Coastal engineering is a sector within civil engineering. This means companies hire us to help them with harbor design and construction; beach nourishment and erosion studies; wave modeling and forecasting, sediment transport modeling; and dredging and pile driving monitoring; among many others.

Monitoring the dredgers in the Moss Landing harbor.

Chilean Columns of Basalt!

The characteristic hexagonal pattern of the basalt columns form after the rock cools.

While on a beach down in Chile, South America the Moss Landing Marine Labs Global Systems class stumbled on a series of interesting rock features.  The low silica rock of Chile flows easily and comes from molten lava, when it cools it contracts and forms.  These cracks that form from cooling are roughly 6-sided, or hexagonal, and can form huge columns as seen at California’s Devils Postpile National Park.  We took the liberty of testing the rock’s structural integrity while trying to climb these amazing columns.  The columns seem man made, but knowing some basic geology helps to determine the origin, even when in another hemisphere from home.

You can tell these columns shifted after the time they were created by the way they tilt to the side.

 

Dozens of Diatoms

By Catherine Drake, Invertebrate Zoology Lab

The last field trip of the fall semester for the Geological Oceanography class was to the Monterey Formation on Toro Road in the Salinas Basin. As we drove up through the hills on the winding road, we came across a grayish cliff that must have spanned about a mile down the road. The students got out of the car, and as we walked along the road, we noted the striations and laminations within the sedimentary layers. What’s especially interesting about these layers is that they are biogenic sediments: they consist of organic particles, usually in the form of skeletal fragments of marine organisms.

The Monterey Formation consists of an incalculable amount of diatoms, which are a type of phytoplankton and are primary producers, meaning they take up carbon dioxide while. Diatoms have siliceous tests, meaning that their cell walls are silica based; so, when diatoms die, they become part of a siliceous ooze and get deposited on the seafloor. Considering that diatoms usually range from 2 to 200 μm and the Monterey Formation spanned almost a mile, which means that there were hundreds of millions of diatoms at the time! Primary production must have been incredibly high during that time period, which was approximately between 11 and 3 million years ago.

Diatoms are phytoplankton that produce oxygen through primary production.

Learning About the Central Coast Through Geological Oceanography

By Catherine Drake, Invertebrate Zoology Lab

Other than a few awesome, albeit too short, trips to the Monterey Bay Aquarium, I hadn’t spent much time in the Central Coast.  So when I moved up here for graduate school at MLML, I didn’t know much about the area; that is, until my MS 141 class.  Geological Oceanography—taught by Dr. Ivano Aiello—involves learning about the formation of minerals and rocks, as well as geological mechanisms such as plate tectonics.  We’ve taken field trips almost every week to various locations along the Central Coast and inland as well.  One of my favorite field trips was our overnight trip to Point Reyes, where we stayed in an old lifeboat station while we observed different types of rock formations.

The lifeboat station was built in 1927 at Chimeny Rock in Point Reyes.

We examined multiple sedimentary rocks both along our journey to the station and also once we had arrived.  One of the depositions we inspected was an outcrop of radiolarian cherts.  These deposits sit underneath about half of the Marin Headlands, are resistant to weathering, and can be up to 200 million years old.  They are comprised of radiolarians, which are protozoans that form siliceous (made of silica) skeletons.  As these organisms decompose, a radiolarian ooze is formed in the deep ocean; over time, deposition occurs along the seafloor, forming the well-bedded radiolarian cherts.

Radiolarian cherts are formed from years of deposition of radiolarian siliceous skeletons on the seafloor.

Igneous rocks were also on our list of stops, as we went to a formation of pillow basalts.  They are formed underwater as lava comes in contact with seawater and cools rapidly.  Basalts are generally aphanitic rocks, meaning that they cool down too quickly for any minerals to form as the magma cools.  As they are created, pillow basalts form ellipsoidal shapes and depict the direction of the lava flow.

Behind the class are pillow basalts, which are igneous rocks formed underwater as lava comes in contact with seawater and rapidly cools down.

It was so surreal to touch igneous and sedimentary structures that formed hundreds of millions of years ago.  Examining these rocks helped me better understand the geological mechanisms involved in their formation.  Not only did these sedimentary depositions and igneous rocks help me become more acquainted with the Central Coast, but they also demonstrated the fact that oceans are integral components to the geologic history of our planet.

Sampling the Seafloor with a Lunar Lander?

Collecting samples from the deep aboard the Research Vessel Point Sur. (photo: E. Loury)

Just like a space rover, this instrument is designed to help us study places that are inhospitable to people.  But rather than the furthest reaches of space,  this corer travels to the depths of the sea to where it collects cores of the mud and sand on the ocean floor.  Geological oceanographers like MLML professor Ivan Aiello (left) can use the samples to learn how different geologic features  in an area formed throughout history – in this case, the study site is Monterey Bay.

On Top of the World at Fremont Peak

(photo: H. Hawk)

The Geological Oceanography class enjoys a panoramic view at the top of Fremont Peak with professor Ivano Aiello.  Geo Oce students got the opportunity to go on lots of trips in the field to experience California’s geology firsthand.  See a picture from another one of their adventures here.

Against the Grain

Jeremiah Brower

by Jeremiah Brower, Geological Oceanography Lab

One of the reasons I love being a Geological Oceanographer is that you can walk along the beaches of Santa Cruz and travel through thousands of years of history in a few short miles. Much of the coastline here is actually made up of shallow marine plankton deposits that have been crushed over the years into a fine silt and sandstone layer that is greater then 150 m thick.

Basically, the coastline of Santa Cruz was once underwater and has been slowly rising through a tectonic process called “uplift” for the better part of the last two hundred thousand years.  Because of uplift, these previously submerged sediment deposits of the continental shelf are now exposed above the ocean, and natural erosion has cut them back to the cliff walls we see today.

Geologists identify this cliff layer we find on our coastline as the ‘Purisima formation’ and date it to the late Pliocene era (1.6-5.3 million years ago, which is young as rocks go, if you can believe it!).  The Purisima formation is structured with thousands of shell fragments from clams and various other plant and animal life forms that used to live on the sea floor. By examining the different layers of the formation you can see when the ocean was more full of life, or when the sea floor was a sort of dessert (just another cool aspect of geologic oceanography).

A certified time detective and rock hunter in action.

No matter where you go in the field, you tend to find that the land has been affected by the ocean. The Santa Lucia range of central California is another great example: it was created by the compaction of millions of marine carbonate shells left behind by various planktonic life forms.

So I suggest that the next time you’re hiking in the mountains or hanging out at the beach with a cold mojito, consider the sand and rocks around you. Most of this planet is covered in water, and that water has affected most of the land we stand on – so don’t be surprised if you’re hiking in Montana and find a shark’s tooth at your feet!

Sand man over and out.