Mark Van Arsdale: What Makes Up an Ecosystem? Part II – Phytoplankton, September 14, 2018

NOAA Teacher at Sea

Mark Van Arsdale

Aboard R/V Tiglax

September 11 – 26, 2018

 

Mission: Long Term Ecological Monitoring

Geographic Area of Cruise: North Gulf of Alaska

Date: September 14, 2018

 

Weather Data from the Bridge

Mostly cloudy, winds variable 10 knots, waves to four feet

58.27 N, 148.07 W (Gulf of Alaska Line)

 

Science Log

What Makes Up an Ecosystem?  Part II Phytoplankton

Most of my students know that the sun provides the foundational energy for almost all of Earth’s food webs.  Yet many students will get stumped when I ask them, where does the mass of a tree comes from?  The answer of course is carbon dioxide from the air, but I bet you already knew that.

Scientists use the term “primary productivity” to explain how trees, plants, and algae take in carbon dioxide and “fix it” into carbohydrates during the process of photosynthesis.  Out here in the Gulf of Alaska, the primary producers are phytoplankton (primarily diatoms and dinoflagellates). When examining diatoms under a microscope, they look like tiny golden pillboxes, or perhaps Oreos if you are feeling hungry.

Primary productivity experiments running on the back deck of the Tiglax.

Primary productivity experiments running on the back deck of the Tiglax.

One of the teams of scientists on board is trying to measure the rates of primary productivity using captive phytoplankton and a homemade incubation chamber. They collect phytoplankton samples, store them in sealed containers, and then place them into the incubator.  Within their sample jars, they inject a C13 isotope.  After the experiment has run its course, they will use vacuum filtration to separate the phytoplankton cells from the seawater.  Once the phytoplankton cells are captured on filter paper they can measure the ratios of C12 to C13. Almost all of the carbon available in the environment is C12 and can be distinguished from C13.  The ratios of C12 to C13 in the cells gives them a measurement of how much dissolved carbon is being “fixed” into sugars by phytoplankton.  Apparently using C14  would actually work better but C14 is radioactive and the Tiglax is not equipped with the facilities to hand using a radioactive substance.

During the September survey, phytoplankton numbers are much lower than they are in the spring.  The nutrients that they need to grow have largely been used up.  Winter storms will mix the water and bring large amounts of nutrients back to the surface.  When sunlight returns in April, all of the conditions necessary for phytoplankton growth will be present, and the North Gulf of Alaska will experience a phytoplankton bloom.  It’s these phytoplankton blooms that create the foundation for the entire Gulf of Alaska ecosystem.

Personal Log

Interesting things to see

The night shift is not getting any easier.  The cumulative effects of too little sleep are starting to catch up to me, and last night I found myself dosing off between plankton tows.  The tows were more interesting though.  Once we got past the edge of the continental shelf, the diversity of zooplankton species increased and we started to see lantern fish in each of the tows.  Lantern fish spend their days below one thousand feet in the darkness of the mesopelagic and then migrate up each night to feed on zooplankton.  The have a line of photophores (light producing cells) on their ventral sides.  When they light them up, their bodies blend in to the faint light above, hiding their silhouette, making them functionally invisible.

A lantern fish with its bioluminescent photophores visible along its belly.

A lantern fish with its bioluminescent photophores visible along its belly.

Once I am up in the morning, the most fun place to hang out on the Tiglax is the flying bridge.  Almost fifty feet up and sitting on top of the wheelhouse, it has a cushioned bench, a wind block, and a killer view.  This is where our bird and marine mammal observers work.  Normally there is one U.S. Fish and Wildlife observer who works while the boat is transiting from one station to the next.  On this trip, there is a second observer in training.  The observers’ job is to use a very specific protocol to count and identify any sea bird or marine mammal seen along the transect lines.

Today we saw lots of albatross; mostly black-footed, but a few Laysan, and one short-tailed albatross that landed next to the boat while were casting the CTD.  The short-tailed albatross was nearly extinct a few years ago, and today is still considered endangered. That bird was one of only 4000 of its species remaining.  Albatross have an unfortunate tendency to follow long-line fishing boats.  They try to grab the bait off of hooks and often are drowned as the hooks drag them to the bottom.  Albatross are a wonder to watch as they glide effortlessly a few inches above the waves.  They have narrow tapered wings that are comically long. When they land on the water, they fold their gangly wings back in a way that reminds me of a kid whose growth spurts hit long before their body knows what to do with all of that height.   While flying, however, they are a picture of grace and efficiency.  They glide effortlessly just a few inches above the water, scanning for an unsuspecting fish or squid.  When some species of albatross fledge from their nesting grounds, they may not set foot on land again for seven years, when their own reproductive instincts drive them to land to look for a mate.

Our birders seem to appreciate anyone who shares their enthusiasm for birds and are very patient with all of my “What species is that?” questions.  They have been seeing whales as well.  Fin and sperm whales are common in this part of the gulf and they have seen both.

A Laysan Albatross

A Laysan Albatross, photo credit Dan Cushing

 

Did You Know?

Albatross, along with many other sea birds, have life spans comparable to humans.  It’s not uncommon for them to live sixty or seventy years, and they don’t reach reproductive maturity until well into their teens.

 

Animals Seen Today

  • Fin and sperm whales
  • Storm Petrels, tufted puffins, Laysan and black-footed and short-tailed albatross, flesh footed shearwater

 

Martha Loizeaux: Spectrophotometers and Eggplant Curry, August 28, 2018

NOAA Teacher at Sea

Martha Loizeaux

Aboard NOAA Ship Gordon Gunter

August 22-31, 2018

Mission: Summer Ecosystem Monitoring Survey
Geographic Area of Cruise: Northeast Atlantic Ocean
Date: August 28, 2018

Weather Data from the Bridge

  • Latitude:  39.487 N
  • Longitude:  73.885 W
  • Water Temperature: 25.2◦C
  • Wind Speed:  13.1 knots
  • Wind Direction: WSW
  • Air Temperature: 26.1◦C
  • Atmospheric Pressure:  1017.28 millibars
  • Depth:  30 meters

Science and Technology Log

spectrophotometer

This is the underwater spectrophotometer!

“Underwater spectrophotometer”… say that 10 times fast!  I was lucky enough to steal a few minutes of Audrey Ciochetto’s time while we admired the views from the fly bridge today.  Audrey works with the Colleen Mouw Lab at the University of Rhode Island.  Her lab studies phytoplankton (you may remember that phytoplankton is plankton that is like a plant) and how light from the sun interacts with plankton.  I bet you never thought about that!  It’s amazing stuff!

Audrey and a graduate student from the lab, Kyle Turner, have brought another cool science tool on board, an underwater spectrophotometer.  The ship has pipes hooked up that take water in from 4 meters under the surface of the ocean at a constant flow.  This water goes into the spectrophotometer and the machine gets to work.  It shines light through the water and measures how the light is absorbed (taken in).  Did you know that light travels in waves?  Different colors of light that you see are different wavelengths.  The spectrophotometer can measure 83 different color wavelengths and what happens to them when they shine on the water.

What does happen to light when it shines into the water?  First of all, the water itself absorbs some of the light.  There are also a lot of tiny things in the water that absorb light.  Can you think of some tiny things that might be in the water? You guessed it again!  Phytoplankton is absorbing some of the light, but also other things like tiny particles and dissolved matter will absorb light.  These items will also scatter the light, making it bounce in different directions.  The underwater spectrophotometer measures that too!

filtering Audrey

Audrey filtering water samples to separate particles and plankton

Audrey and Kyle spend some of their day taking samples of the water and filtering out the plankton and particles, leaving only the dissolved matter.  They will also bring some sea water samples back to their lab to separate the phytoplankton from the rest of the particles. By separating all of these factors, scientists can get an idea of how each of these components in the water are responding to light.

The goal of this work is to understand what satellites are seeing.  Scientists rely on satellites out in space to take pictures of what’s happening on Earth.  These satellites can detect the light from the sun shining on Earth.  They can see some color wavelengths as they are absorbed or scattered by different things on our planet.  With the work that Audrey and Kyle are doing, we can better understand the satellite pictures of the ocean and what they mean.  We can understand what’s in the ocean by looking at what the sunlight is doing when it touches the water.  Pretty incredible, right?

The Design of Experiments

Hearing all of these brilliant ideas from Audrey got me thinking about how creative scientists must be to design experiments and investigations to answer questions.
Remember the hypothesis example that Chief Scientist Harvey mentioned in his interview?  It was an idea that scientists came up with after they used monitoring data to discover a pattern of lower populations of herring (fish).

Hypothesis:  “Increasing haddock populations lead to a lower stable state of herring because haddock feed on herring eggs.”

fish stomach contents

Scientists can study the stomach contents of fish to learn what they are eating. Photo courtesy of The Fisherman Magazine.

How would you design an experiment to test this?
Well, the real scientists who did this work examined the stomach contents of haddock to see how much of their diet consisted of herring eggs!  Would you have thought of that?
It was interesting to read about this study in a scientific journal called PNAS (it stands for Proceedings of the National Academy of Sciences), “Role of egg predation by haddock in the decline of an Atlantic herring population.” By Richardson et. al.

Get creative and start thinking of your own ideas to answer questions you have about the world!

 

 

Scientist Spotlight – Tamara Holzwarth-Davis, Physical Science Technician

Tamara is the physical science technician for NOAA National Marine Fisheries Service (NMFS) at Woods Hole.  A technician is someone who is an expert on the equipment and technology used by the scientists.  Today I had a chance to ask Tamara some more questions about her work.

Me – Tell me more about your job.
Tamara – I provide quality control for all of the data brought back by all of the ships involved in our study.  A lot of it is statistical analysis of data [this means looking at data and making sure that it makes sense and is accurate].  I calibrate sensors [make sure they are accurate], process data, and write reports based on the data we find.  We create a yearly atlas of information based on our data that anyone can use to look for trends (such as changes in plankton populations).  I also maintain and coordinate equipment that is needed for the studies.

Me – What part of your job with NOAA did you least expect to be doing?Tamara – I least expected to be so involved with plankton!  I used to do only the hydrography (water chemistry and physical properties) but now I am also involved with plankton data collection.

Tamara on watch

Tamara keeps track of a lot of different things during her watch.

Me – How do you help other people understand and appreciate NOAA’s work?
Tamara – I write the reports and make data available to the public.  People can be reassured that quality control is in place in our monitoring and the data is as accurate as possible.  It is my job to make sure of it!

Me – What do you love about going out to sea?
Tamara – I love the experience of being out at sea and meeting new people!

Personal Log

Our days on the ship are spent collecting data at stations, storytelling and watching the water on the fly bridge, catching up on work, watching sunrises and sunsets.  I’ve been pleasantly surprised by the comfort and commodities (like comfy mattresses and hot showers) and especially, THE FOOD!

food

The food options are outstanding. One night we had king crab legs and tuna steaks.

Margaret chef

Margaret is the best chef EVER.

Here on NOAA Ship Gordon Gunter, we have a wonderful steward staff (cooks and kitchen managers), Margaret and Paul. They always have smiles on their faces when you walk in for meal time and are happy to spread their cheerfulness.  There is always an amazing menu with many items to choose from.  As a vegetarian, I have been blown away by all of the delicious veggie options.  But there is plenty of meat for the carnivores too!  There are always a variety of snacks available as well as healthy options.

Margaret makes homemade cookies and pies, guacamole, crab salad, and eggplant curry, just to name a few.  We all sit down for meals together and share stories.  And there is always dessert!

Did You Know?

Water absorbs red light first.  So, if a fish has red scales when it’s out of the water, under water he will look brown and blend in to his surroundings.  All of the red light will have already been absorbed by the water and there won’t be enough left to reflect off the fish’s scales!

squirrelfish

A squirrelfish can blend in to its surroundings under water. Since it is a red fish, it is hard to see its color since the water has already absorbed the red light from the sun. Photo courtesy of NOAA.

Animals Seen Today

Common dolphins, green sea turtle, brown booby bird, larval hake, larval flounder, larval sea bass, jellyfish

brown booby

Bobby the brown booby stayed with our ship for several hours.

jellyfish jar

A jellyfish we caught in the plankton net!

Martha Loizeaux: Cool Science Tools and Drifter Buoy! August 26, 2018


Susan Dee: Microscopic Sea Life – Days 1-4, May 24, 2018

NOAA Teacher at Sea
Susan Dee
Aboard NOAA Ship Henry B. Bigelow
May 23 – June 7, 2018

Mission:  Spring Ecosystem Monitoring Survey

Geographic Area of Cruise:  Northeastern Coast U.S.
Date: May 24, 2018
Weather Data from Bridge
Latitude: 40°32′
Longitude: 070°45′
Sea Wave Height:  1-2 feet
Wind Speed:  12 knots°
Wind Direction: west
Viability: unrestricted
Air Temperature:  13.5°C
Sky: Few clouds

Science and Technology Log

Tuesday, May 22, I arrived at Newport Naval Base and boarded NOAA Ship Henry B. Bigelow to begin my Teacher at Sea journey by staying overnight on a docked ship.   Day 1 was filled with many new experiences as we headed out to sea.  The Henry B. Bigelow is part of a fleet of vessels commissioned to conduct  fishery surveys. To learn more about the Henry B. Bigelow,  check out this website:  Henry B. Bigelow. The objective of this cruise is to access the hydrographic, planktonic and pelagic components of North East U.S. continental shelf ecosystem.  The majority of the surveys we will take involve  the microbiotic parts of the sea –  phytoplankton, zooplankton and mesoplankton.  Plankton are small microscope organisms in the oceans that are extremely important to the entire Earth ecosystem.  These organisms are the foundation of the entire ocean food web. By studying their populations. scientists can get an accurate picture of the state of  larger ocean organism populations.

Susan and ship

Henry B. Bigelow

Leaving Newport Harbor

Leaving Newport Harbor

Before leaving the dock, I met with Emily Peacock from Woods Hole Oceanographic Institute (WHOI) to learn how to run an Imaging Flow Cytobot instrument that uses video and flow cytometric technology to capture images of phytoplankton. The IFCB was developed by Dr Heidi Sosik and Rob Olsen (WHOI) to get a better understanding of coastal plankton communities. The IFCB runs 24 hours a day collecting sea water and continuously measuring phytoplankton abundance.  Five milliliters of sea water are analyzed every 20 minutes and produces the images shown below.

Imaging Flow CytoBot

Emily Peacock teaching the usage of the Imaging Flow CytoBot (IFCB)

 

Imaging Flow Cytobot IFCB

Imaging Flow Cytobot (IFCB)

phytoplankton

Images of Phytoplankton taken by IFCB

The science party on board is made up of scientists from National Marine Fisheries Service (NMFS) part of NOAA Fisheries Division. The chief scientist, Jerry Prezioso, works out of Narragansett Lab and the lead scientist, Tamara Holzworth Davis, is from the Woods Hole Lab, both from the NOAA Northeast Fisheries Science Center.  Other members of the Science Party are Seabird/Marine Mammal observers and a student  from Maine Maritime Academy.  The Crew and scientist group work together to coordinate sampling stations. The crew gets the ship to the site and aid the scientists in deploying instruments. The scientists collect the data and samples at each station.  The Crew and scientists work together to find the best and most efficient sea route to each  sampling site. Note all the stops for specimen collection on map below. There definitely  has to be a plan!

map of proposed route

Proposed Cruise Track and Survey Locations

 

Personal Log

Because research instrument deployment is done 24 hours a day, the NOAA Corps crew and scientists are divided into two shifts. I am on watch 1200 – 2400 hours, considered the day shift. This schedule is working good for me. I finish duty at midnight, go to sleep till 9:00 AM and rise to be back on duty at noon. Not a bad schedule. Due to clear weather and calm seas, the ship headed east out of Newport Harbor towards the continental shelf and started collecting samples at planned stops.   I joined another group of scientists  observing bird and marine mammal populations from the flying bridge of the ship. Humpback whales and basking sharks breached  several times during the day

It has only been two days but I feel very acclimated to life at sea. I am not seasick, thanks to calm seas and the patch. Finding the way around the ship is getting easier- it is like a maze. Spotting a pod of humpback whales breaching and basking sharks was a highlight of the day. My Biology students back at May River  High School scored great on End of Course Exam. Congratulations May River High School Sharks! Thinking of y’all.

school logo

Love My SHARKS!

Chelsea O’Connell-Barlow: Full Steam Ahead, August 30, 2017

NOAA Teacher at Sea

Chelsea O’Connell-Barlow

Aboard NOAA Ship Bell M. Shimada

August 29 – September 12, 2017

 

Mission: Pacific Hake Survey

Geographic Area of Cruise: NW Pacific Ocean

Date: 8/30/2017

 

Weather Data from the Bridge:

Latitude: 48.472837N

Longitude: -124.676694W

Temperature 59 F

Wind 9.7 knots

Waves 3-5 feet

Science and Technology Log

We have not started fishing yet because we are heading to our first transect off the western coast of the Haida Gwaii archipelago. I thought this would be a perfect time to introduce another research project that is gathering data on the Shimada. One of my roommates, Lynne Scamman, is on-board researching Hazardous Algal Blooms (HABs).

Lynne in Chem lab

Lynne Scamman running wet chemistry tests and identifying phytoplankton.

  1. What are Hazardous Algal Blooms?

They are large numbers of phytoplankton, either diatoms or dinoflagellates, who produce toxins. Phytoplankton are essential to the ecosystem because they produce half of the global oxygen. However under certain circumstances these organisms reproduce rapidly, skyrocketing the population, this is a bloom. Some of these phytoplankton produce toxins. When the populations are low the toxins aren’t a big deal. However, when a bloom of phytoplankton that produce toxins occurs there can be health concerns for organisms exposed to the toxins. We have to consider the marine food chain and something called bioaccumulation. Phytoplankton along with zooplankton create the base of the marine food web. Organisms who eat toxin producing phytoplankton retain the toxin in their body. Then any organism who eats them will also hold that toxin. You can see how the toxin would accumulate along the food chain and potentially hold serious side effects for organisms with high levels of toxin.

  1. Why is research being done on HABs?

HABs are becoming a problem for humans along the coasts and in the Great Lakes. Basically all of the factors that contribute to the increase in HABs are a product of human impact. Global climate change, increased nutrient pollution and global sea trade are all factors contributing to the rise in Hazardous Algal Blooms. We want to monitor so that eventually we will be able to predict when, where and why the HABs will occur.

  1. Why are YOU studying HABs?

One day I walked into my college biology lab and met a guest instructor who specializes in all things phytoplankton related. I was blown away by the complexity that some of these single celled organisms held. The professor shared a few species names and I started investigating. The species that grabbed my attention is called Nematadinium armatum. This organism has a rudimentary eye called a melanosome and nematocysts for hunting, again this is pretty impressive for an organism made of one cell. Once I learned about the variety in this microscopic world and how influential they were to the health of the entire ocean, I knew that I wanted to learn more.

Personal Log

I am still figuratively pinching myself every few hours at just how amazing this experience is to participate in first hand. Yesterday we left the dock of Port Angeles at 10am and the boat hasn’t slowed down since. We did drills to ensure that all aboard knew where to go in case of fire and if we needed to abandon ship. Part of the abandon ship drill is to make sure that everyone has and can get into their Immersion Suit aka “Gumby Suit.” This suit is amazing! This portion of the Pacific is quite cold and the Immersion suit would keep you warm and buoyant until a rescue can occur.

OCB Gumby

Trying on the Immersion suit.

After our drills several of the science crew went up to the Flying Bridge to look for marine mammals. We were cruising between Cape Flattery, Washington and Vancouver Island, British Columbia with high hopes of seeing activity. WOW, we lucked out. We spotted 17 Humpback whales, 2 Harbor porpoise and 2 Dall’s porpoise. We are also seeing several types of sea birds but I am still brushing up with the Sibley to id birds from this area.

Shimada Flags

The Shimada under two flags as it enters Canadian waters.

 

Did You Know?

The island cluster that we are heading to had a name change at the end of 2009. What was formerly called Queen Charlotte Islands is now called Haida Gwaii. This name change came as part of a historic reconciliation between British Columbia and Haida nation. Haida Gwaii translated means “island of the people.”

Haida Gawaii

Map of Haida Gawaii area.

Amanda Dice: Ending Week 1 at Line 8, August 26, 2017

NOAA Teacher at Sea

Amanda Dice

Aboard Oscar Dyson

August 21 – September 2, 2017

 

Mission: Juvenile Pollock Fishery Survey

map cropped

Oscar Dyson moves across the Shelikof Straight to collect the Line 8 samples

Geographic area of cruise: Western Gulf of Alaska

Date: August 26, 2017

Weather Data: 13.2 C, cloudy with light rain

Latitude 57 36.6 N, Longitude 155 .008 N

 

 

Science and Technology Log

As part of this survey, the scientists onboard collect data from what is known as “Line 8”. This is a line of seven sampling stations, positioned only a few miles apart, near the southern opening of Shelikof Straight between Kodiak Island and the Alaskan Peninsula. Water samples are taken at different depths at each sampling station to measure several different properties of the water. This study is focused on profiling water temperature and salinity, and measuring the quantities of nutrients and phytoplankton in the water.

IMG_0988

The CTD rosette is lowered into the water using a winch – as seen from above.

To collect this data, a conductivity and temperature at depth (CTD) instrument is lowered into the water. This instrument can take water samples at different depths, by using its eleven canisters, or Niskin bottles. The water collected in the Niskin bottles will be used to determine the nutrient quantities at each station. The rosette of Niskin bottles also has sensors on it that measure phytoplankton quantities, depth, temperature, and how conductive the water is. Scientists can use the readings from conductivity and temperature meters to determine the salinity of the water.

Each Niskin bottle has a stopper at the top and the bottom. The CTD goes into the water with both ends of each Niskin bottle in the open position. The CTD is then lowered to a determined depth, depending on how deep the water is at each station. There is a depth meter on the CTD that relays its position to computers on board the ship. The survey team communicates its position to the deck crew who operate the winch to raise and lower it.

IMG_1164

Niskin bottles are lowered into the water with the stoppers at both ends open.

When the CTD is raised to the first sampling depth, the survey crew clicks a button on a monitor, which closes the stoppers on both ends of Niskin bottle #1, capturing a water sample inside. The CTD is then raised to the next sampling depth where Niskin bottle #2 is closed. This process continues until all the samples have been collected. A computer on board records the depth, conductivity and temperature of the water as the CTD changes position. A line appears across the graph of this data to show where each sample was taken. After the Niskin bottles on the CTD are filled, it is brought back onto the deck of the ship.

IMG_1173

They let me take control of closing the Niskin bottles at the sampling depths!

CTD screen cropped

I used this screen to read the data coming back from the CTD and to hit the bottle to close each Niskin bottle. The purple horizontal lines on the graph on the right indicate where each one was closed.

Water is collected through a valve near the bottom of each Niskin bottle. A sample of water from each depth is placed in a labeled jar. This study is interested in measuring the quantity of nutrients in the water samples. To do this it is important to have samples without phytoplankton in them. Special syringes with filters are used to screen out any phytoplankton in the samples.

Screen Shot 2017-08-26 at 8.28.56 PM

Syringes with special filters to screen out phytoplankton are used to collect water samples from the Niskin bottles.

The “Line 8” stations have been sampled for nutrient, plankton, and physical water properties for many years. The data from the samples we collected will be added to the larger data set maintained by the Ecosystems and Fisheries-Oceanography Coordinated Investigations (Eco-FOCI), Seattle, Washington. This NOAA Program has data on how the marine ecosystem in this area has changed over the last few decades. When data spans a long time frame, like this study does, scientists can identify trends that might be related to the seasons and to inter-annual variation in ocean conditions. The samples continue to be collected because proper nutrient levels are important to maintaining healthy phytoplankton populations, which are the basis of most marine food webs.

 

IMG_1171

Collecting water samples from a Niskin bottle.

Personal Log

As we travel from one station to the next, I have some time to talk with other members of the science team and the crew. I have really enjoyed learning about places all over the world by listening to people’s stories. Most people aboard this ship travel many times a year for their work or have lived in remote places to conduct their scientific studies. Their stories inspire me to keep exploring the planet and to always search for new things to learn!

Did you know?

Niskin bottles must be lowered into the water with both ends open to avoid getting an air bubble trapped inside of them. Pressure increases as depth under water increases. Niskin bottles are often lowered down below 150 meters, where the pressure can be intense. If an air bubble were to get trapped inside, the pressure at these depths would cause air bubble to expand so much that it might damage the Niskin bottle!

DJ Kast, Interview with Megan Switzer and the Basics of the CTD/ Rosette, May 28, 2015

NOAA Teacher at Sea
Dieuwertje “DJ” Kast
Aboard NOAA Ship Henry B. Bigelow
May 19 – June 3, 2015

Mission: Ecosystem Monitoring Survey
Geographical area of cruise:
Gulf of Maine
Date: May 28, 2015, Day 11 of Voyage

Interview with Student Megan Switzer

Chief Scientists Jerry Prezioso and graduate oceanography student Megan Switzer

Chief Scientist Jerry Prezioso and graduate oceanography student Megan Switzer

Megan Switzer is a Masters student at the University of Maine in Orono. She works in Dave Townsend’s lab in the oceanography department. Her research focuses on interannual nutrient dynamics in the Gulf of Maine. On this research cruise, she is collecting water samples from Gulf of Maine, as well as from Georges Bank, Southern New England (SNE), and the Mid Atlantic Bight (MAB). She is examining the relationship between dissolved nutrients (like nitrate and silicate) and phytoplankton blooms. This is Megan’s first research cruise!

In the generic ocean food chain, phytoplankton are the primary producers because they photosynthesize. They equate to plants on land. Zooplankton are the primary consumers because they eat the phytoplankton. There are so many of both kinds in the ocean. Megan is focusing on a particular phytoplankton called a diatom; it is the most common type of phytoplankton found in our oceans and is estimated to contribute up to 45% of the total oceanic primary production (Yool & Tyrrel 2003). Diatoms are unicellular for the most part, and a unique feature of diatom cells is that they are enclosed within a cell wall made of silica called a frustule.

Diatom Frustules. Photo by: 3-diatom-assortment-sems-steve-gschmeissner

Diatom Frustules. Photo by: Steve Schmeissner

Diatoms! PHOTO BY:

Diatoms! Photo by: Micrographia

The frustules are almost bilaterally symmetrical which is why they are called di (2)-atoms. Diatoms are microscopic and they are approximately 2 microns to about 500 microns (0.5 mm) in length, or about the width of a human hair. The most common species of diatoms are: Pseudonitzchia, Chaetocerous, Rhizosolenia, Thalassiosira, Coschinodiscus and Navicula.

Pseudonitzchia. Photo by National Ocean Service

Pseudonitzchia. Photo by National Ocean Service

Thalassiosira. Photo by: Department of Energy Joint Genome Institute

Thalassiosira. Photo by: Department of Energy Joint Genome Institute

Photo of Coscinodiscus by:

Photo of Coscinodiscus

Diatoms also have ranges and tolerances for environmental variables, including nutrient concentration, suspended sediment, and flow regime.  As a result, diatoms are used extensively in environmental assessment and monitoring. Furthermore, because the silica cell walls are inorganic substances that take a long time to dissolve, diatoms in marine and lake sediments can be used to interpret conditions in the past.

In the Gulf of Maine, the seafloor sediment is constantly being re-suspended by tidal currents, bottom trawling, and storm events, and throughout most of the region there is a layer of re-suspended sediment at the bottom called the Bottom Nepheloid Layer. This layer is approximately 5-30 meters thick, and this can be identified with light attenuation and turbidity data. Megan uses a transmissometer, which is an instrument that tells her how clear the water is by measuring how much light can pass through it. Light attenuation, or the degree to which a beam of light is absorbed by stuff in the water, sharply increases within the bottom nepheloid layer since there are a lot more particles there to block the path of the light. She also takes a water sample from the Benthic Nepheloid Layer to take back to the lab.

Marine Silica Cycle by Sarmiento and Gruber 2006

Marine Silica Cycle by Sarmiento and Gruber 2006

Megan also uses a fluorometer to measure the turbidity at various depths. Turbidity is a measure of how cloudy the water is. The water gets cloudy when sediment gets stirred up into it. A fluorometer measures the degree to which light is reflected and scattered by suspended particles in the water. Taken together, the data from the fluorometer and the transmissometer will help Megan determine the amount of suspended particulate material at each station. She also takes a water sample from the Benthic Nepheloid layer to take back to the lab. There, she can analyze the suspended particles and determine how many of them are made out of the silica based frustules of sinking diatoms.

 This instrument is a Fluorometer and is used to measure the turbidity at various depths. Photo by: DJ Kast

This instrument is a Fluorometer and is used to measure the turbidity at various depths. Photo by: DJ Kast

She collects water at depth on each of the CTD/ Rosette casts.

Rosette with the 12 Niskin Bottles and the CTD. Photo by DJ Kast

Rosette with the 12 Niskin Bottles and the CTD. Photo by DJ Kast

Rosette with the 12 Niskin Bottles and the CTD. Photo by DJ Kast

Rosette with the 12 Niskin Bottles and the CTD. Photo by DJ Kast

Up close shot of the water sampling. Photo by DJ Kast

Up close shot of the water sampling. Photo by DJ Kast

CTD, Rosette, and Niskin Bottle basics.

The CTD or (conductivity, temperature, and depth) is an instrument that contains a cluster of sensors, which measure conductivity, temperature, and pressure/ depth.

Here is a video of a CTD being retrieved.

Depth measurements are derived from measurement of hydrostatic pressure, and salinity is measured from electrical conductivity. Sensors are arranged inside a metal housing, the metal used for the housing determining the depth to which the CTD can be lowered. Other sensors may be added to the cluster, including some that measure chemical or biological parameters, such as dissolved oxygen and chlorophyll fluorescence. Chlorophyll fluorescence measures how many microscopic photosynthetic organisms (phytoplankton) are in the water. The most commonly used water sampler is known as a rosette. It is a framework with 12 to 36 sampling Niskin bottles (typically ranging from 1.7- to 30-liter capacity) clustered around a central cylinder, where a CTD or other sensor package can be attached. The Niskin bottle is actually a tube, which is usually plastic to minimize contamination of the sample, and open to the water at both ends. It has a vent knob that can be opened to drain the water sample from a spigot on the bottom of the tube to remove the water sample. The scientists all rinse their bottles three times and wear nitrile or nitrogen free gloves to prevent contamination to the samples.

On NOAA ship Henry B. Bigelow the rosette is deployed  from the starboard deck, from a section called the side sampling station of this research vessel.

The instrument is lowered into the water with a winch operated by either Adrian (Chief Boatswain- in charge of deck department) or John (Lead Fishermen- second in command of deck department). When the CTD/Rosette is lowered into the water it is called the downcast and it will travel to a determined depth or to a few meters above the ocean floor. There is a conducting wire cable is attached to the CTD frame connecting the CTD to an on board computer in the dry lab, and it allows instantaneous uploading and real time visualization of the collected data on the computer screen.

 

CTD data on the computer screen. Photo by: DJ Kast

CTD data on the computer screen. Photo by: DJ Kast

The water column profile of the downcast is used to determine the depths at which the rosette will be stopped on its way back to the surface (the upcast) to collect the water samples using the attached bottles.

Niskin Bottles:

Messenger- The manual way to trigger the bottle is with a weight called a messenger. This is sent down a wire to a bottle at depth and hits a trigger button. The trigger is connected to two lanyards attached to caps on both ends of the bottle.  When the messenger hits the trigger, elastic tubing inside the bottle closes it at the specified depth.

Todd with the manually operated Niskin Bottle. Photo by: DJ Kast

Todd holding a messenger to trigger the manually operated Niskin Bottle. Photo by: DJ Kast

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Todd with the manually operated Niskin Bottle. Photo by: DJ Kast

Todd with the manually operated Niskin Bottle. Photo by: DJ Kast

Manual CTD fully cocked and ready to deploy. Photo by DJ Kast

Manual CTD fully cocked and ready to deploy. Photo by DJ Kast

Here is a video of how the manual niskin bottle closes: https://www.youtube.com/watch?v=qrqXWtbUc74

The other way to trigger Niskin bottles is electronically. The same mechanism is in place but an electronic signal is sent down the wire through insulated and conductive sea cables (to prevent salt from interfering with conductivity) to trigger the mechanism.

Here is a video of how it closes electronically: https://www.youtube.com/watch?v=YJF1QVe6AK8

Conductive Wire to CTD. Photo by DJ Kast

Conductive Wire to CTD. Photo by DJ Kast

Photo of the top of the CTD. Photo by DJ Kast

Photo of the top of the CTD showing the trigger mechanism in the center. Photo by DJ Kast

Top of the Niskin Bottles to show how the white wires are connected to the top.

Top of the Niskin Bottles shows how the lanyards are connected to the top. Photo by DJ Kast

The pin on the bottom is activated when an electronic signal is sent through the conductive sea cables. Photo by DJ Kast

The pin on the bottom is activated when an electronic signal is sent through the conductive sea cables. Photo by DJ Kast

Using the Niskin bottles, Megan collects water samples at various depths. She then filters water samples for her small bottles with a syringe and a filter and the filter takes out the phytoplankton, zooplankton and any particulate matter. She does this so that there is nothing living in the water sample, because if there is there will be respiration and it will change the nutrient content of the water sample.

Filtering out only the water using a syringe filter. Photo by DJ Kast

Filtering out only the water using a syringe filter. Photo by DJ Kast

Photo by: DJ Kast

Syringe with a filter on it. Photo by: DJ Kast

This is part of the reason why we freeze the sample in the -80 C fridge right after they have been processed so that bacteria decomposing can’t change the nutrient content either.

Diatoms dominate the spring phytoplankton bloom in the Gulf of Maine. They take up nitrate and silicate in roughly equal proportions, but both nutrients vary in concentrations from year to year. Silicate is almost always the limiting nutrient for diatom production in this region (Townsend et. al., 2010). Diatoms cannot grow without silicate, so when this nutrient is used up, diatom production comes to a halt. The deep offshore waters that supply the greatest source of dissolved nutrients to the Gulf of Maine are richer in nitrate than silicate, which means that silicate will be used up first by the diatoms with some nitrate left over. The amount of nitrate left over each year will affect the species composition of the other kinds of phytoplankton in the area (Townsend et. al., 2010).

The silica in the frustules of the diatom are hard to breakdown and consequently these structures are likely to sink out of the euphotic zone and down to the seafloor before dissolving. If they get buried on the seafloor, then the silicate is taken out of the system. If they dissolve, then the dissolved silicate here might be a source of silicate to new production if it fluxes back to the top of the water column where the phytoplankton grow.

Below are five images called depth slices. These indicate the silicate concentration (rainbow gradient) over a geographical area (Gulf of Maine) with depth (in meters) latitude and longitude on the x and y axis.

Depth slices of nitrate and silicate. Photo by: This is the type of data Megan is hoping to process from this cruise.

Depth slices of nitrate and silicate. Photo by:  GOMTOX at the University of Maine
This is the type of data Megan is hoping to process from this cruise.