The oceanography of the Monterey Bay National Marine Sanctuary is influenced by the California Current, a 1,200-kilometer (745-mile) broad and 300-meter (985-feet) deep surface current that transports water of subarctic origin southward along the North American coast at 15 to 30 centimeters (5.9 to 11.8 inches) per second (cm/s). Beneath this surface current and within about 100 kilometers of the coast, the California Undercurrent transports waters of subtropical origin northward at about four cm/s. In winter, this current surfaces, where it mixes with California Current waters and is called the Inshore Countercurrent, or Davidson Current.

Together, these currents are termed the California Current System, and the sanctuary lies wholly within this system. Thus, the surface and intermediate-depth water masses in the sanctuary are a mixture of subarctic Pacific water with low salinity and cool temperatures together with warmer, saltier Pacific Equatorial water. The pelagic organisms of the sanctuary originate and travel north- or southwards in these different water masses.

Three oceanographic seasons were originally described for Monterey Bay in the 1940s and are still in common use today:

  • the upwelling period from early spring to late summer (February to July), when surface waters are cool
  • the oceanic, or California Current, period from late summer to early fall (August to October), characterized by wind relaxation
  • the Davidson Current period from late fall to late winter (November to January) characterized by winter storm conditions

During the spring and summer, upwelling occurs along much of the coast within the sanctuary, but Point Año Nuevo and Point Sur “anchor” areas of especially strong upwelling. These upwelling centers are readily observed in satellite images as cool zones, typically 3 to 5 ºC (37.4 to 41 ºF) cooler than waters 100 kilometers offshore.

Satellite images often show a tongue of cool water originating at the Año Nuevo center and flowing southwards across the mouth of Monterey Bay. This upwelling plume spins off eddies circulating both offshore and within the bay.

In the north bay, northward flow and lack of wind (the Santa Cruz mountains block upwelling-favorable winds) create an upwelling shadow characterized by strong thermal stratification and warm surface waters. In summer, this area flushes slowly and is often brown with very high phytoplankton biomass. (It has been called the “armpit” or “incubator” region of the bay.)

The upwelling center near Point Sur is generally cooler and more extensive than that near Año Nuevo. During strong upwelling conditions (persistent northwesterly winds), these cool waters can merge, forming a continuous band of upwelled water from north of Monterey Bay to south of Point Sur.

Varying degrees of iron limitation have been measured in the coastal waters of central California during the summer upwelling seasons. Iron limitation is most common and severe in waters removed from continental shelf sources of iron. Thus, areas with a wide continental shelf (e.g., Monterey Bay and the shelf to the north) tend to have waters that are iron-replete compared to areas with a narrow shelf (south of Monterey Bay). Iron-replete and iron-limited waters tend to differ in the associated phytoplankton communities and relative biomass at many trophic levels.

While the seasonal changes in the coastal ocean and Monterey Bay are important, longer-term interannual variations, principally El Niño events, also affect local physical and biological systems. During the 1982-1983 El Niño (one of the strongest in the last century), for example, dramatic changes were observed in the phytoplankton composition of Monterey Bay, such as an increased relative abundance of dinoflagellates and tropical species and a decreased abundance of diatoms.

During the 1992-1993 El Niño, total phytoplankton abundance and primary production rates measured in March 1992 were reduced by factors of three to four compared to March 1990. In addition, the increase in water temperature during an El Niño brings exotic species of southerly or offshore origin that are usually not found in the sanctuary.

Sanctuary offshore waters are in relatively good condition, but nearshore coastal areas, harbors, lagoons, estuaries and tributaries show a number of problems, including elevated levels of coliform bacteria, detergents, oils, nitrates, sediments and persistent pesticides such as DDT and toxaphene. These contaminants can have a variety of biological impacts – including bioaccumulation, reduced recruitment of anadramous species and transfer of human pathogens – as well as interference with recreational uses due to beach closures.

Phytoplankton blooms, including harmful algal blooms, have increased in frequency and distribution worldwide since 1980. The frequency of such blooms may be increasing with nutrient enrichment from agricultural and urban storm runoff as well as sewage effluent.


Spatial and Temporal Variability in Oceanographic and Meteorological Forcing along Central California
Researchers with the United States Geological Survey (USGS) analyzed more than 20 years (1980-2002) of hourly deep-water buoy data from off central California to investigate long-term trends and the behavior of the measured oceanographic and meteorological variables during different climatic regimes. Statistically significant differences were observed in the monthly mean significant wave height, dominant wave period, sea-level barometric pressures, sea-surface water temperature, and wind speed and direction during normal, La Niña and El Niño months. In addition to these monthly differences, statistically significant long-term trends in monthly mean significant wave height, dominant wave period, sea-level barometric pressures, sea-surface water temperature and wind speed were observed.

Monterey Bay Ocean Time Series Observations
Researchers at the Monterey Bay Aquarium Research Institute (MBARI) are studying the biogeochemical response of the central California ecosystem to climate and ocean variability. They are exploring the dynamic connections among physical, chemical and biological processes. This program has found that since 1998, ocean temperatures have fallen; the California Current has strengthened; and subsurface nitrate, surface chlorophyll and primary production have all increased due to a change in the Pacific Decadal Oscillation (PDO). This PDO-associated cooling makes it difficult to detect global warming in Monterey Bay.

Monterey Bay Aquarium Incoming Seawater Monitoring
As part of the Monterey Bay Aquarium’s ongoing water quality program, incoming seawater is monitored with both spot measurements and continuously on a five-minute interval using in-situ sensor technology. Data on water temperature, dissolved oxygen and nutrients have detected both seasonal events, such as upwelling, and periodic events, such as El Niños.

Center for Integrated Marine Technologies (CIMT)
CIMT is an interdisciplinary coastal research consortium that integrates data collected via remote sensing, moorings and ship-board surveys in the Monterey Bay region. CIMT uses these technologies to investigate linkages among coastal upwelling, nutrient delivery, phytoplankton and organisms at higher trophic levels (squid, fishes, seabirds, sea turtles, seals and whales).

Monterey Bay Microbial Observatory
Small, single-celled planktonic microbes represent the most abundant organisms in the world’s oceans. The goal of this study is to describe the microbes of Monterey Bay and correlate the presence and absence of particular groups with other physical, chemical and biotic variables.

Characterization of Geologic and Oceanographic Conditions at Pleasure Point
The USGS is compiling baseline geologic and oceanographic information on the coast and inner shelf off Pleasure Point in Santa Cruz County. This study will provide high-resolution topography of the coastal bluffs and bathymetry of the inner shelf out to water depths of 20 meters. In addition, the spatial and temporal variation in waves will be documented. These data will provide the baseline data needed for future studies directed toward predicting the impacts of stabilization on the sea cliffs, beach and nearshore sediment profiles; natural rock reef structures; and offshore habitats and resources.

Photo Library

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Project Database


Are the Waters Along the Central California Coast and Monterey Bay Getting Colder?

There are indications that waters along the California coast are getting colder. Here we briefly examine three questions related to this change. First, how evident is this cooling along the central California coast and in Monterey Bay? Second, when did the change to cooler conditions occur locally? And third, why is it happening?


California El Niños

Unusual physical and ecological conditions in the California Current differ during individual El Niño and La Niña events. The project compares large-scale forcing associated with tropical El Niño and La Niña events, to describe and understand differences in the west coast response to these events.


Center for Integrated Marine Technologies: Wind to Whales

The Center for Integrated Marine Technologies&#39 (CIMT) mission is to create a coastal ocean observing and forecasting system that provides a scientific basis for the management and conservation of Monterey Bay, and serve as a model for all of California\’s coastal marine resources and the U.S. Integrated Ocean Observing System (IOOS).


Center for Integrative Coastal Observation, Research and Education (CICORE)

The CSU Center for Integrative Coastal Observation, Research and Education (CI-CORE) is a distributed coastal observatory for applied coastal research and monitoring in the nearshore (<100 m water depth) along the entire California coastline.


Characterization of geologic and oceanographic conditions at Pleasure Point, Santa Cruz County

A USGS study is underway to characterize the coastal bluffs, inner shelf morphology and wave conditions at Pleasure Point in Santa Cruz County.


CSCAPE: Collaborative Survey of Cetacean Abundance and the Pelagic Ecosystem.

CSCAPE is a collaboration between the National Marine Fisheries Service and the National Marine Sanctuary Program to assess the abundance and distribution of marine mammals and to characterize the pelagic ecosystem out to ~300 nautical miles off the U.S. West Coast.


In-situ Measurements of Turbidity Currents in the Monterey Submarine Canyon

For the first-time, scientists direclty measured the speed and character of turbidity currents in Monterey Canyon.


MARS: Passive Acoustic Monitoring (Hydrophone)

The marine 'soundscape' is a continuously changing mosaic of sounds that originate from living organisms (communication and foraging), non-living natural processes (breaking waves, rain) and human activities (shipping, construction, and resource extraction). Listening to sound in the sea is a rich exploration of the marine environment, which includes some of the ways in which human activities may intersect with marine life.


MBARI Time Series (MBTS) Program

The oceanography of the MBNMS has received considerable study over the past 50 years. The California Cooperative Oceanic Fisheries Investigations (CalCOFI) began in 1949 to study the declining sardine fisheries off the North American west coast but over the decades it evolved and expanded in scope. This project describes how the Biological Oceanography Group at MBARI has conducted a focused program of observation on CalCOFI Line 67, within and offshore of Monterey Bay in the MBNMS.


Monterey Bay Aquarium Incoming Seawater Monitoring

As part of the Monterey Bay Aquarium’s ongoing water quality program incoming seawater is monitored with both spot measurements and continuously on a 5minute interval using in situ sensor technology. Both seasonal events, such as upwelling, and periodic events, such as El Niño are visible in the data record.


Monterey Bay Microbial Observatory

Small, single-celled planktonic microbes represent the most abundant organisms in the world's oceans. This study aims to describe the microbes of the Monterey Bay and create a model for understanding marine microbial communities in general.


Nearshore water monitoring of oxygen and pH in southern Monterey Bay

A decade-long time series of water quality parameters indicated that the nearshore, shallow subtidal was regularly inundated with cold, low oxygen and low pH waters.


Nutrient Sources to Support the Gulf of the Farallones Food Web

The goal of this ongoing project is to determine whether nutrients from San Francisco Bay impact the rich food web of the Gulf of the Farallones in order to assess if anthropogenic changes in the estuary will have management implications for the coastal ecosystem.


Ocean Margin Ecosystems Group for Acidification Studies (OMEGAS)

This is a three-year, NSF-funded study on the impacts of acidic ocean waters on two ecologically important species (sea urchins and mussels) in the California Current Large Marine Ecosystem.


Ocean observing in the Monterey Bay National Marine Sanctuary: CalCOFI and the MBARI time series

This report introduces the CalCOFI and the MBARI programs as they relate to each other and oceanography within the MBNMS. A report (see below) includes a brief review of MBNMS oceanography with summary graphs, and also provide introductory links to the extensive websites and detailed research papers of both programs.


Phytoplankton toxins in critical prey species in the Monterey Bay National Marine Sanctuary

Domoic acid (DA) is natural toxin produced by certain species of phytoplankton. When consumed by higher predators (e.g., marine mammals, birds, fishes), DA can cause sickness or death. This project studies samples from current research programs and past studies to the distribution and transmission of this toxin within the food web of Monterey Bay.


Pioneer Seamount Ocean Acoustic Observatory

A vertical array of four hydrophones was installed on Pioneer Seamount to passively monitor the Pacific Ocean in the region south of San Francisco, CA.


Santa Cruz Ocean Observing Platform (SCOOP)

The primary goals of the Santa Cruz Ocean Observing Platform (SCOOP) are to establish and maintain a long-term dataset of weather and oceanographic measurements at the Santa Cruz Wharf that is accessible to both researchers and the public.


SCOPE: Simulations of Coastal Ocean Physics and Ecosystems

We propose to model the coastal upwelling ecosystem within the Monterey Bay National Marine Sanctuary (MBNMS) with high spatial (kms) and temporal (days) resolution.


Spatial and Temporal Variability in Oceanographic and Meteorologic Forcing along Central California: 1980-2002

High-resolution hourly data from 8 NOAA buoys deployed since the early 1980's off Central California were analyzed to improve our understanding of spatial and temporal variability of oceanographic and meteorologic forcing along the coastline.


Tagging of Pacific Predators (TOPP)

The Tagging of Pacific Pelagics (TOPP) research program aims to understand the migration patterns of large predators in the North Pacific basin and how these animals act and interact in their open ocean habitats. By using satellite tagging techniques, TOPP researchers follow the movements of different species across multiple trophic levels (i.e., the food web) and in relation to physical oceanographic features in order to piece together a whole ecosystem picture.


West Coast Obs and the Partnership for Interdisciplinary Studies of Coastal Oceans (PISCO): Oceanography component

The Partnership for Interdisciplinary Studies of Coastal Oceans (PISCO) Oceanographic monitoring program began in 1999. The project uses nearshore moorings to monitor ocean temperature at 18 sites between Pigeon Point and San Simeon, with ocean currents also measured at 4 and salinity at 1. Project data support PISCO’s ecological studies in kelp forests and rocky intertidal habitats in the MBNMS.