Arterial Gases and Hemoglobin in Diving Seals

By Rubicon Foundation editorial team

5 min read · 1 November 2026

Research on arterial gases and hemoglobin in diving animals examines how blood carries oxygen and carbon dioxide during breath-hold dives. The Weddell seal offers a way to study these processes in a mammal that dives without breathing underwater, making its physiology relevant to questions about human diving, oxygen stores and the limits of breath-holding.

What do arterial gases reveal during a dive?

Arterial blood carries oxygen from the lungs to tissues and returns carbon dioxide towards the lungs. Measuring its gas tensions—the partial pressures of dissolved oxygen and carbon dioxide—helps researchers track how the blood’s respiratory state changes across a dive or during recovery.

Those measurements are not a direct readout of every tissue’s oxygen supply. Blood values reflect the combined effects of ventilation, circulation and gas exchange, while organs may differ in blood flow and oxygen demand. Researchers therefore interpret arterial samples alongside the timing and conditions of a dive.

For divers, the distinction matters: a single oxygen value cannot describe the whole body’s condition. The underlying question is how the circulation maintains essential functions as breathing stops and oxygen stores are drawn down.

Why measure hemoglobin as well as oxygen?

Most oxygen in blood is carried bound to hemoglobin inside red blood cells; only a small fraction is dissolved in plasma. Hemoglobin concentration therefore helps define how much oxygen the blood can carry, while arterial oxygen tension describes the pressure of oxygen dissolved in the blood.

The two measures answer different questions. Oxygen tension helps characterise the conditions under which oxygen loads onto hemoglobin and is released; hemoglobin concentration contributes to the blood’s carrying capacity. Neither alone determines how much oxygen reaches a particular organ, which also depends on blood flow and tissue demand.

That distinction connects animal physiology to diving medicine. Human breath-hold diving and compressed-gas diving have different hazards, but both make oxygen delivery, circulation and the response to changing gas conditions central concerns.

How can researchers study a freely diving seal?

Work on free-ranging divers must relate physiological measurements to behaviour without treating a brief sample as a complete account of a dive. A study may consider when blood is sampled, whether the animal is diving or recovering, and how the measurement relates to the surrounding dive sequence. The title of this research area points to arterial blood measurements made in freely diving Weddell seals.

Blood sampling and gas analysis require careful handling. Exposure to air, delays and changes in temperature can alter a sample, while the animal’s activity and recovery state can affect what the sample represents. Interpreting the measurement depends on preserving its context.

Arterial oxygen tension: a measure of dissolved oxygen pressure in arterial blood.
Arterial carbon dioxide tension: a measure relevant to ventilation and carbon dioxide removal.
Hemoglobin concentration: a factor in the blood’s oxygen-carrying capacity.
Dive and recovery timing: context needed to interpret a blood sample.

What can seal physiology tell human divers?

Weddell seals are not small models of human divers. They have specialised adaptations for prolonged breath-holding, and their responses cannot be transferred directly to people. Their value is comparative: studying how a diving mammal manages oxygen and carbon dioxide can help frame questions about the basic physiology shared across mammals and the adaptations that differ.

This work sits within a broader field that includes decompression, asphyxia, diver performance and the effects of pressure. Each addresses a different part of the underwater environment. Arterial-gas research focuses on blood and respiratory exchange, helping distinguish oxygen availability from problems caused by pressure changes or impaired breathing.

For scientific divers and clinicians, the useful lesson is methodological as much as biological: measurements need to be read in context, and animal results need cautious translation. Decisions about a person’s fitness to dive or symptoms after diving belong with a diving-medicine physician.

Frequently asked questions

What is arterial gas tension?

It is the partial pressure of a gas dissolved in arterial blood. Oxygen and carbon dioxide tensions help describe blood gas status, but they do not by themselves measure oxygen delivery to every tissue.

Why study hemoglobin in a diving animal?

Hemoglobin carries most of the oxygen in blood. Its concentration helps researchers assess oxygen-carrying capacity alongside gas tensions, circulation and the timing of a dive.

Can seal physiology guide human diving medicine?

It can inform comparative questions about oxygen transport and breath-holding, but seals have specialised adaptations. Their physiology should not be treated as a direct basis for individual human medical advice; consult a diving-medicine physician about personal concerns.

An original research-library explainer written by the Rubicon editors. It is not a summary of a specific publication.