marine bio afternoon class Oceanography and Marine Biology Lecture Notes: Carbon Cycles, Currents, and Plankton Dynamics

Introductory Logistics and Scheduling

• Day One Challenges: The speaker notes that the first day of the course typically contains an intensive amount of material to cover.

• Scheduling: No field trips have been scheduled yet, requiring students to "grind through" the lecture material.

• Content Obligations: There is a specific amount of mandated content to cover, preventing the class from solely focusing on practical activities in the syrup.

The Carbon Cycle (Question 6)

• Definition and Movement: The carbon cycle describes the movement of carbon through the atmosphere, the earth, and all trophic levels.

• Physical versus Biological Components:     * Physical: Involves atmospheric and aqueous carbon.     * Biological: Carbon is sequestered and trapped in biological organisms through designated processes.

• Most Abundant Form: Carbon is found in its most abundant form as the gas carbon dioxide ($CO_2$).

• Carbon Sequestration: Carbon enters the food chain through the fundamental biological process of photosynthesis.     * Sources and Sinks: The atmosphere functions as a carbon source, while "sinks" basically trap carbon.     * Oceanic Primary Producers: In the ocean, photosynthesis is performed primarily by Algae, specifically Phytoplankton, which form the base of all ocean food chains.     * The Ocean as a Sink: The ocean is the largest carbon sink on the planet.

Ocean Carbon Equilibrium and Acidification

• Aqueous Interconversion: At the water's surface, gaseous $CO_2$ interconverts with and becomes dissolved in seawater (aqueous form).

• Carbon Equilibrium Equation: Once dissolved, carbon enters a buffering equilibrium based on pH and available compounds. The reaction occurs forwards and backwards:     * $CO_2 + H_2O \rightleftharpoons H_2CO_3 \rightleftharpoons H^+ + HCO_3^- \rightleftharpoons 2H^+ + CO_3^{2-}$     * Carbonic Acid: Produced when $CO_2$ dissolves in sea water ($H_2CO_3$).     * Bicarbonate: Carbonic acid dissociates a hydrogen ion to form bicarbonate ($HCO_3^-$).     * Carbonate: Bicarbonate loses another hydrogen ion to become carbonate ($CO_3^{2-}$).

• Ocean Acidification: Pumping an excess of $CO_2$ into the oceans increases the hydrogen ion concentration ($H^+$), making the water more acidic and forcing the equilibrium equation to the right. This reduces the amount of bicarbonate available for shell-building organisms.

• Effect of Photosynthesis on pH: Photosynthesis extracts $CO_2$, forcing the equation back to the left, which increases bicarbonate availability and raises the pH of the seawater.

• Dependency on Bicarbonate: Many organisms precipitate carbon out of solution to form shells and skeletons:     * Corals (particularly stony corals).     * Echinoderms (e.g., sea urchins, sand dollars).     * Mollusks.     * Arthropods.     * Foraminifera (Forams).

• Coral Physiology:     * Stony Coral: Only the outermost layer is alive. It consists of thin tissue covering a calcium carbonate skeleton.     * Coralite: The little cup in which the individual polyp sits.     * Polyp: A biological structure related to sea anemones and jellyfish.     * Enzymatic Conversion: Corals use an enzyme to convert bicarbonate into their bodies, concentrating it in the coralite to precipitate out the exoskeleton.

Carbon Movement to the Deep Sea

• Surface Activity: Most photosynthesis and initial carbon trapping occur at the ocean surface.

• Diel Vertical Migration: This is a daily process where organisms migrate to the surface at night to feed and then return to the depths, effectively dragging carbon back down into the deep sea.

• Global Warming Implications: For the benefit of global warming mitigation, it is preferable to have carbon sequestered in the deep sea.

Ocean Currents and Tides

• The Engine of Currents: The primary engine driving ocean currents is Wind.

• The Driver of Wind: The Sun is the ultimate driver of wind. Solar energy heats the Earth unevenly due to the angle of sunlight hitting the atmosphere. This creates areas of high and low pressure.

• Trade Winds: Hot air rises at the Equator and colder air moves in to displace it, creating consistent winds at approximately $30^{\circ}$ North and South latitude.

• The Role of Tides: Tides are driven by the gravitational pull of the Moon and the Sun.     * The Earth rotates within a "bulge" of water kept in place by the sun and moon.     * Daily Tides: Most places have two high tides and two low tides daily.     * The Gulf of Mexico: The Gulf typically has only one high and low tide per day (diurnal) because it is not fully connected to the open ocean, and the water takes a full day to cycle in and out. The tidal range in the Gulf is very small, leading to a tiny intertidal zone.

• The Coriolis Effect: This effect dictates the direction of air and water masses, not the energy behind them.     * In the Northern Hemisphere, objects are deflected to the right (clockwise motion).     * In the Southern Hemisphere, objects are deflected to the left (counter-clockwise motion).     * Gyres: These circulation patterns form large loops or gyres in the ocean basins.

Heat Distribution and Ecosystem Impact

• Heat Transport: Currents distribute thermal energy around the globe.     * The Gulf Stream: Transports massive amounts of heat to Western Europe. Without it, regions like Scandinavia, England, Germany, and Amsterdam (lying on the same latitude as Hudson Bay, Canada) would be Arctic tundras with polar bears.

• Current Boundaries:     * Warm Water Currents: Typically hit the Eastern boundaries of continents (Western side of ocean basins), dragging tropical conditions further north or south (e.g., Florida Keys, Bermuda).     * Cold Water Currents: Typically hit the Western boundaries of continents (Eastern side of ocean basins).

• Biological Consequences:     * Coral reefs are mostly concentrated on the Western boundaries of ocean basins.     * Kelp forests are found on Western continental coasts due to cold water currents.

• Exceptions (South America): Despite being tropical, Brazil lacks major coral reef systems due to the Amazon and Orinoco Rivers. These rivers pump monumental amounts of fresh water and sediment (runoff) into the Atlantic, smothering habitats and reducing water clarity.

Ocean Geography and Seafloor Topography (Question 9 & 10)

• Five Oceans: As of 2021, five oceans are recognized: Pacific, Atlantic, Indian, Arctic, and Southern.     * The Southern Ocean: Recognized for the first time in 2021. It is defined by the $60^{\circ}$ latitude line and strong currents that circumnavigate Antarctica, keeping it oceanographically distinct.

• Seafloor Features: The seafloor is not flat; it contains mountains, volcanoes, crests, and slopes.     * Mid-Atlantic Ridge: A major underwater mountain range formed by seafloor spreading.     * Trenches: Created by subduction, where one continental plate is forced under another.

• Continental Shelf: The shallow part of the seafloor attached to continents (approximately $200\text{ feet}$ deep).     * Passive vs. Active Margins: The Gulf of Mexico is a passive zone with no volcanic activity and a wide continental shelf (extending $30$ to $50\text{ miles}$ offshore). California has an active/subduction zone with a very narrow continental shelf and deep underwater canyons.

Plate Tectonic Theory

• Tectonic Plates: The Earth's crust is broken into plates that move via convection currents of magma in the Earth's mantle.

• Historical Geography:     * Pangaea: The original supercontinent.     * Gondwana: The southern supercontinent after Pangaea split.     * Laurasia: The northern supercontinent.

• Seafloor Growth: The Atlantic Ocean is currently getting larger at a rate of approximately $2\text{ inches}$ per year.

• Isthmus of Panama: Formed about $3\text{ million}$ years ago, closing the gap between the Atlantic and Pacific. This deflected equatorial currents north, powering the current Gulf Stream.

Classification of Marine Organisms (Questions 13 - 15)

• By Location:     * Benthic: Organisms that live in or on the seafloor (the benthos), ranging from the shelf to the Abyssal Plain.     * Pelagic: Organisms that live in the water column.

• By Movement:     * Nekton: Pelagic swimmers that can swim against currents and move independently (e.g., sharks, dolphins, fish).     * Plankton: Pelagic drifters that cannot swim against ocean currents in a meaningful way (e.g., jellyfish, larvae).     * Neuston: Organisms that live at the air-sea interface, staying right at or under the surface (e.g., Portuguese Man O' War).

Types and Lifecycle of Plankton

• Phytoplankton: Primary producers that photosynthesize. They produce half of the Earth's oxygen and regulate climate via the "biological pump."

• Zooplankton: Heterotrophic animals that do not photosynthesize.

• Duration in Planktonic State:     * Holoplankton: Organisms that spend their entire life cycle as plankton (e.g., diatoms, copepods).     * Meroplankton: Organisms that spend only part of their life cycle as plankton, usually the larval stage (e.g., crab and fish larvae).

• Larval Feeding Strategies:     * Planktotrophic: Larvae that feed on other planktonic organisms.     * Lecithotrophic: Larvae that survive on a yolk sac/finite energy reserve before metamorphosing.

Specific Planktonic Groups

• Dinoflagellates:     * Possess two flagella.     * Responsible for Harmful Algal Blooms (HABs).     * Red Tides: High-toxicity events often caused by nutrient runoff (e.g., drainage from Lake Okeechobee into the Gulf).     * Ciguatera: A toxin produced by dinoflagellates that bioaccumulates up the food chain (from parrotfish to barracuda/grouper) and is not destroyed by cooking.     * Bioluminescence: Some species light up when waves crash or the sand is disturbed.     * Zooxanthellae: Beneficial dinoflagellates that live in coral tissues in a mutualistic relationship.

• Copepods:     * The most common zooplankton; they are holoplankton.     * Characterized by two long antennae and jerky movements.     * Reynolds Number: For a copepod, the Reynolds number makes water feel functionally like Jell-O, requiring high energy to move.

• Crustacean Larval Stages:     * Nauplia: The first stage for crabs, shrimp, and barnacles (one eye, few appendages).     * Zoea: Characterized by a large eye, big nose, and a pointy spine.     * Megalopa: Starts to look like a crab but with the abdomen still extended.

Questions & Discussion

• Student Question: Is the seafloor flat?

• Answer: No, it has mountains, trenches, and various topographical features like the Mid-Atlantic Ridge and continental shelves.

• Student Question/Discussion: What drives the wind?

• Answer: The sun heating the atmosphere unevenly creates pressure differences, which causes air mass movement.

• Reference to Field Work: Students were instructed to meet at the dock early tomorrow for "plankton toes" using nets of different sizes to gather samples for microscopic study. They were warned not to handle catfish due to their spines.

• Location Reference: The class will meet at the pier/dock past the Coast Guard Building on the Dauphin Island Sea Lab map (near the aquarium and Wiese Marine Science Hall)." , "title": "Oceanography and Marine Biology Lecture Notes: Carbon Cycles, Currents, and Plankton Dynamics"}