Monterey Bay Aquarium Research Institute

California Current Logbook
Day 8: Lines and currents
February 11, 2012

A few days back, Jason Smith, a graduate student at Stanford University who's done a few of these longer expeditions, commented that a research cruise was a lot like the classic Bill Murray movie Groundhog Day—you keep living the same day over and over again, and you can't leave, so all you can do is try to do a better job each day. So goes Day 8: pre-dawn CTD cast, the increasingly rapid cyclonic circulation of samplers round the rosette, another spectacular sunrise, on to the next station.

The Sierra de la Laguna rises out of the morning mist at the southern tip of Baja California.

The next station, which we arrived at before noon, was on "line P18." The creatively named P18—the "P" stands for Pacific—is a line of study designated by the World Ocean Circulation Experiment (WOCE), a multi-national research project organized to observe the physical processes of the ocean. P18 runs due south down the 110 degrees West longitudinal line from Baja California all the way to Antarctica. We'll make three sampling stations along our transit down P18 from 22°N to 21°N—one degree is 60 nautical miles, which is about 110 kilometers—before reversing course and heading back to La Paz in the Gulf of California.

This strategy of drawing lines out into the ocean and then repeatedly sampling along them is an incredibly effective way to study the circulation of waters around the ocean basins. At this point I imagine you're thinking, "Is he really going to keep talking about lines?" And I can see why a discussion on geometric figures formed by points moving along a fixed direction might be slightly less than captivating. But please bear with me, when we get to the part about what crosses the lines and, better still, how we know what "it" is, you'll be glad you stayed.

Second mate Paul Ban doing his "ship work"—the work he does when he's not steering the vessel. It's business only in those headphones. I can assure you he's absolutely not listening to the Misfits.

If you've been reading these logs closely-which I think is the best way to read them, though I might have a bias—you may have noticed I keep using the word "waters" (as opposed to water, singular). This plural usage isn't just idiomatic; oceanographers refer to distinctive masses of water in the larger ocean, for example "sub-tropical sub-surface waters" or "Gulf of California waters." But how can one tell one water apart from another? As it turns out, when water is at the ocean's surface, and therefore able to exchange gases with the air, it acquires a very specific set of salinity and temperature characteristics that allow oceanographers to track it. (Spookier even, is water that happened to be at the surface in the 1940s can be tracked by the residual fallout from exploded atomic bombs.)

So now that we know how to track water masses, the next question is how these masses get to moving. The most significant currents are wind generated. The California Current, which flows towards the equator from the pole down the western coast of North America, and is part of the larger North Pacific Gyre, is one such current. The California Undercurrent (CU)—also referred to as the Davidson Current when it surfaces in the winter, and the current we've been studying—is different. The wind does have an effect on the CU, but its effect is predominantly on how deep or shallow the CU is. What drives the CU is pressure—the waters in the CU effectively run downhill.

To grossly (but not erroneously) oversimplify the process, water in the north is colder, and therefore denser than the warmer southern waters. So, it takes more warm water to equalize the pressure of the cold northern water, and water basically "stacks up" higher in the south. Up at the top of this "pile" of water, the pressure is greater in the south, so the water flows downhill to the north. The sketch below that Curt Collins drew of a manometer helped clarify the point for me. And so the water starts slowly rolling its way up the coast; by Curt's rough calculations it takes water around one to two years to get from the tip of the Baja peninsula up to the Monterey Bay.

Curt Collins sketched this manometer to illustrate the pressure gradient between northern and southern waters along the eastern Pacific boundary. The right, shorter, column represents the colder, denser water in the north.
Curt Collins, a truly inspired and inspiring oceanographer.

We'll reach our southern-most destination tonight sometime after midnight. After that we'll likely only have two or three sampling stations before pulling into port. Tonight's sunset ordained Chris Wahl as witness to the green flash, and with only one more at-sea sunset left, everyone's sure to be lined up on the deck this evening for one last chance to glimpse the elusive flash.

A satisfactory consolation for missing the green flash..

—Dana Lacono

 

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 Equipment

R/V Western Flyer

The R/V Western Flyer is a small water-plane area twin hull (SWATH) oceanographic research vessel measuring 35.6 meters long and 16.2 meters wide. It was designed and constructed for MBARI to serve as the support vessel for ROV operations. Her missions include the Monterey Bay as well as extended cruises to Hawaii, Gulf of California and the Pacific Northwest.

CTD Rosette

The CTD measures conductivity (which helps determine salinity), temperature, and depth. This particular CTD runs profiles of the water column (surface to bottom) and along the way, collects discrete water samples (at specific predetermined depths) using the rosette of niskin bottles. Each bottle can collect a water sample. The transmissometer measures the number of particles in the water and the oxygen sensors tell us how much dissolved oxygen is present. Both of these instruments go onto the CTD rosette and give us a profile of the water column.

Optical Profiler (PRR)

The optical profiler is equipped with an hyperspectral radiometer which measures downwelling irradiance and upwelling radiance, a CTD, and two AC9's which measure absorption and beam attenuation over nine wavelengths (1 uses filtered seawater while the other uses raw seawater). It also measures backscatter at six wavelengths and fluorescence at two wavelengths.

Fast Repetition Rate Fluorometer

This unique instrument measures the photosynthetic properties of phytoplankton continuously while the ship is in motion. This greatly increases the amount of data as well as the area that can be surveyed.

Underway CTD

An underway CTD is used to map several physical parameters of the ocean's surface. As the ship travels, this instrument takes one sample every 20 seconds. The data recorded includes the ship's location, the ocean's salinity, temperature, and water clarity, and the amount of fluorescence produced by phytoplankton. By continually taking measurements, a line of values along the ship's course is created, illustrating when the ship crosses from one water type to another. The underway CTD is an important complement to the CTD rosette; because each CTD rosette deployment is miles away from the last, the data from the underway CTD measurements help to will indicate whether the rosette CTD sampling spot is representative of the area.

Underway pCO2

Like the underway CTD, the underway pCO2 continually measures the partial pressure of CO2 in the ocean along the course of the Western Flyer. "Partial pressure" is a way in which to measure the amount of CO2 in the seawater. Increasing levels of CO2 in the ocean increase the water's acidity.


 Crew

R/V Western Flyer

Ian Young
Master


 

George Gunther
Relief Captain, Legs 1 & 2


 

Matt Noyes
Chief Engineer


 

Andrew McKee
First Mate, Legs 1 & 2


 

Shaun Summer
Relief First Engineer


 

Paul Ban
Second Mate, Legs 1 & 2


 

Olin Jordan
Oiler


 

Craig Heihn
Relief Deckhand


 

Jason Jordan
Relief Deckhand


 

Dan Chamberlain
Electronics Officer


 

Patrick Mitts
Steward


 

 Research Team

Francisco Chavez
Chief Scientist
MBARI

Francisco Chavez has been managing an ocean observing program at MBARI for more than two decades, gathering a time-series of ocean parameters that have provided insight to how the ocean responds to large-scale climate variability. His work focuses on interpreting observations made locally in terms of processes that are happening globally, and he has performed comparative studies in other ocean basins.

Tim Pennington
Research Specialist
MBARI

Tim works in MBARI's Biological Oceanography Group running their local shipboard programs, all of which are directed at understanding interplay between the physics, chemistry, and biology in the ocean off California. Their Monterey Bay Time Series (MBTS) cruises have been conducted in and offshore of Monterey Bay every two to three weeks since 1989. The Studies of Ecological and Chemical Responses to Environmental Trends (SECRET) cruise series extended the MBTS work 320 kilometers offshore into the California Current along CalCOFI Line 67, with more than 39 quarterly cruises since 1997. This cruise work and complimentary mooring, satellite, ROV, AUV and modelling data have enabled the development of a rich view of the biogeochemical dynamics of the coastal ocean on several spatial (Monterey Bay, upwelling system, California Current) and temporal (weather event, seasonal, interannual, even decadal) scales.

Gernot Friederich
Research Specialist
MBARI

Gernot has been involved in the study of nutrient and carbon fluxes in highly productive regions of the oceans. Most of this work has been conducted in coastal upwelling regions, and he has participated in some high latitude studies. He is also interested in the chemical transformations that occur at the boundaries of oxygenated and sub-oxic or anoxic waters. To aid the study of these highly variable oceanic systems, he has developed and automated chemical methods and water sampling equipment. He has recently worked on the design and implementation of autonomous shipboard seasurface chemistry mapping systems and buoy mounted instrumentation for the measurement of the partial pressure of carbon dioxide.

Erich Rienecker
Instrumentation/Marine Operations Technician
MBARI

An alum of the Biological Ocean Group, Erich now is the instrumentation technician at MBARI and will be responsible for the operation and maintenance of the scientific sampling equipment used on this cruise.

Marguerite Blum
Collaborator
MBARI

Marguerite Blum is a collaborator from University of California, Santa Cruz. She is assisting Gernot Friederich and Tim Pennington with biogeochemical samples to search for differences in the pCO2, DIC, alkalinity, and macronutrients from the previous Gulf of California cruise. This will be her 41st cruise with the Chavez group.

Dana Lacono
Administrative Assistant
MBARI

Dana works in the Information and Technology Dissemination (ITD) group at MBARI where he performs administrative duties and creates web pages such as the one you are looking at now. On this cruise he will be assisting the science team as needed and writing the cruise logs. This is his first research expedition, and he is as excited as can be.

A.J. Limardo
Research Assistant
MBARI

A.J. Limardo received a B.S. in Biology from the University of Georgia, and is currently applying to the University of California, Santa Cruz Ocean Sciences Department to pursue a Ph.D. In the Worden Laboratory at MBARI, A.J. is currently exploring phytoplankton ecology and phylogenetics. During this cruise, he will be investigating the distribution and abundance of Bathycoccus, a genus of pico-eukaryotic algae.

Monique Messié
Postdoctoral Fellow
MBARI

Monique works on phytoplankton and its links with physics and higher trophic levels, using a combination of satellite data, model outputs and in situ datasets. During the cruise she will be helping with the collection and analysis of water samples, including nutrients and oxygen measurements.

Chris Wahl
Research Technician
MBARI

Chris works in the Chavez lab on moorings, gliders, and instrumentation for various projects and was recruited by MBARI's Marine Operations division to help operate the CTD for the first leg of this expedition. He received a B.S. in Mechanical Engineering from University of California, Berkeley and later a M.S. in Engineering Science from University of California, San Diego.

Haibin Zhang
Postdoctoral Fellow
MBARI

Haibin works in the molecular ecology group at MBARI. He received his Ph.D. in marine biology from the Chinese Academy of Sciences, Institute of Oceanology. Haibin's research interests include ecology, evolution, and genetic conservation of marine invertebrates. He uses molecular tools to examine gene flow of natural populations in order to understand the effect of environment factors (light, pressure, oxygen, salinity, and temperature) on population diversity and genetic structure.

Carmen Castro
Collaborator
Higher Council for Scientific Investigations, Spain

Carmen is a chemical oceanographer from Instituto de Investigaciones Marinas from Vigo,Spain. She studies the environmental control of nutrients and carbon in the upwelling regions of NW Iberian Peninsula and California. In this cruise, she will be collecting water samples for analysing the alongshore distribution of total organic carbon.

Curt Collins
Collaborator
Naval Postgraduate School

Curt Collins is a sea-going descriptive physical oceanographer. Convinced by Nan Bray (now Australia's Chief of Marine Research) to make some measurements of the deep flows at the entrance to the Gulf of California in the early 1990s, Curt has since collaborated a number of times with Mexican colleagues including a Fulbright fellowship at Universidad Autónoma de Baja California in Ensenada in 1994/5. Curt is looking forward to helping to collect and analyze the CTD data during this cruise. In addition, he will conduct laboratory analyses of seawater conductivity to assure the accuracy of the team's salinity observations.

Martín Hernández Ayón
Collaborator
Universidad Autónoma de Baja California

Martín Hernández-Ayón is a chemical oceanographer. His research is focused on the inorganic carbon system, ocean acidification and biogeochemistry in the coastal regions of Baja California, the Sea of Cortez, the subtropical region where the oxygen minimum zone is located and, more recently, the Gulf of Mexico.

Gabriela Y. Cervantes
Graduate Student
Universidad Autónoma de Baja California

Gaby is a graduate student in the coastal oceanography program at the University of Baja California in Ensenada, Mexico. She is doing her graduate studies on the dynamics of CO2 in seawater from a coastal monitoring site known as Ensenada Station.

Jason Smith
Graduate Student
Stanford University

Jason is a fifth-year Ph.D. student at Stanford University. His work focuses on how upwelling and other factors alter the distribution and activity of the microorganisms responsible for nitrification. On this cruise Jason's work will focus on ammonium dynamics; specifically, determining the magnitude of ammonia incorporation and oxidation in the photic zone and how it alters estimates of new and regenerated production.




Last updated: Feb. 27, 2012