Understanding Environmental Changes in Our Deep Oceans
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Chapter 1: The Stability of the Deep Ocean
Beneath the ocean's surface lies a tranquil and dark realm that represents one of the most stable environments on Earth. Changes in this environment are typically gradual. It is a cold habitat where temperatures remain steady and immense pressures are a given. Scientists are now scrutinizing this unique area for subtle indicators of global climate change. Given that natural fluctuations in deep-sea conditions are minimal, researchers can effectively isolate these variations to comprehend the extensive implications of human-induced alterations. Consequently, the deep sea serves as a crucial laboratory for observing our planet's health.
As we descend through the ocean, the initial 600 feet make up the photic zone, where sunlight penetrates. Below that lies a layer extending down 2,500 feet, shrouded in perpetual twilight, ultimately leading to complete darkness. This region, known as the thermocline, experiences a sharp decline in temperature. At depths exceeding 12,000 feet, we enter the abyss, where temperatures hover around 37 degrees Fahrenheit (3 degrees Celsius). While the Arctic may experience temperatures exceeding 100 degrees, the abyss remains near freezing, displaying remarkable stability even amidst extreme weather patterns that affect the surface.
Change at the deep ocean floor is nearly imperceptible. For instance, when an anchor is dropped from a ship, it may create a small impact crater on the seabed. However, if one were to return after 50 years, the crater would appear unchanged. Time flows slowly in these stable and unchanging deepwater environments, making them ideal for tracking subtle changes caused by our activities on the surface.
Temperature and Salinity: Key Drivers
Two essential factors that define the environmental conditions in the deep oceans are temperature and salinity. These components also create a connection between the deep ocean and the surface through thermohaline circulation.
In the North Atlantic, cold, salty water descends into the abyss. This process may occur in the Labrador Sea or between Greenland and Scotland. As this water sinks from the surface, it feeds into a deep ocean current known as the “global conveyor belt,” which drives the Atlantic Meridional Overturning Circulation (AMOC). The Gulf Stream is a product of the AMOC.
Overturning circulation refers to the movement of water from the surface to the seafloor and back again, a process also termed thermohaline circulation. The term “thermo” indicates that cold water is denser than warm water, while “haline” signifies that saltwater is denser than freshwater. When cold saline water becomes denser than its surroundings, it sinks. This process initiates a journey lasting up to 1,600 years before the water resurfaces in the North-Central Pacific Ocean.
Changes in temperature and salinity in the deep ocean are influenced by surface conditions. Therefore, alterations at the surface eventually permeate into the deep oceans.
Monitoring the Deep Ocean Environment
Gathering data from the deep oceans poses challenges, as historical ocean temperature records are primarily based on surface observations. However, for the past 20 years, automated profiling floats known as Argo have been collecting data on temperature and salinity from the surface down to 6,500 feet. Prior to the implementation of Argo stations, measurements from the deep ocean were limited and infrequent.
A study published on August 17, 2020, in Nature Climate Change (Silvy et al.) utilized Argo data in conjunction with earlier information to analyze various climate models. This research aimed to examine the impacts of human-induced climate change on the deep oceans, revealing significant temperature and salinity shifts that surpass natural variability. The initial signs of climate change were detected in the deep Southern Ocean between 1980 and 1990, while substantial changes in the Northern Hemisphere's waters have only emerged in the last decade.
The modeling indicates that up to 50% of deep ocean environments currently exhibit the effects of climate change, with projections suggesting that by 2080, up to 80% of the world's oceanic ecosystems will be affected.
The Importance of Monitoring Changes
The shifts in temperature and salinity in the deep oceans are significant. Oceans influence global weather patterns, sustain billions of people, and serve as the primary heat reservoir from global warming. Approximately 90% of excess heat from climate change has been absorbed by the oceans. This heat is crucial, as healthy oceans depend on thermohaline-driven circulation to maintain oxygen levels. Without these circulation systems, deep ocean ecosystems risk becoming anoxic, leading to mass die-offs and the formation of dead zones.
As temperature and salinity in the deep oceans deviate from natural variations due to climate change, the stability of deepwater ecosystems, known for their environmental resilience, faces uncertainty. The response of these ecosystems to such changes remains largely unknown, as does the potential impact on thermohaline circulation, a vital aspect of deep-sea life. Understanding the breadth of the problem is the first step, and ongoing research highlights emerging challenges, though it is merely the beginning.
The first video, "Pathways Connecting Climate Changes to the Deep Ocean Webinar Series," discusses how climate change affects deep ocean environments and the implications for global ecosystems.
The second video, "Is the Deep Ocean Creepy?" explores the unique characteristics and mysteries of deep ocean life, shedding light on its importance to our planet's health.