The highlight of the Seiko Prospex "Marinemaster 1968 Heritage JAMSTEC Collaboration Limited Edition" is its expressive gradient dial.

Seiko Prospex has announced the "Marinemaster 1968 Heritage JAMSTEC Collaboration Limited Edition," featuring a gradient dial inspired by the "shipping routes" created by icebreakers breaking through the Arctic Ocean ice. The entire dial has a texture reminiscent of cracked ice, and is adorned with a blue gradient reminiscent of a clear ocean. This article will discuss the background of this project, the relationship between Seiko and JAMSTEC, and the overall quality of the watch, including its wearability.

Check out this limited edition Marine Master model, themed around navigating the Arctic Ocean while cutting through ice.

　This time, we'll focus on the "Marinemaster 1968 Heritage JAMSTEC Collaboration Limited Edition," a collaboration model with the Japan Agency for Marine-Earth Science and Technology (JAMSTEC). This model is based on a design that pays tribute to the 1968 model from Seiko Prospex's high-end "Marinemaster" series, and the dial depicts the scene of cutting through the ice-covered Arctic Ocean. The center of the dial is a blue inspired by the deep, clear sea, and the appeal lies in the gradient that changes to white on both sides to represent the sea ice. Let's delve deeper into the lineage of the base model for this watch, the relationship between JAMSTEC and Seiko, and the reason for the Arctic Ocean theme, as well as the wearing experience and the finishes of each part.

Let's review the lineage leading up to the "Marinemaster 1968 Heritage."

　Seiko's diver's watches were born in 1965 and have a history of being used early on by the Japanese Antarctic Research Expedition, which helped to build their reliability. The model released in 1968 featured a world-class high-beat movement of 10 vibrations per second, enabling it to withstand air dives to 300 meters. It also possessed various elements that greatly influenced the design of subsequent Seiko diver's watches, such as a robust and sharp case, lines from the case sides to the lugs, and a crown at the 4 o'clock position.

　The "Marinemaster 1968 Heritage" is inspired by this 1968 model.

　The name Marine Master signifies that it is the flagship model of Seiko's current diver's watches. Seiko has tested the Marine Master not only in development testing equipment but also in the ocean, proving that it has the performance worthy of a flagship model. One of the most famous examples is the 2014 test in which saturation diving models (Ref. SBBN013 and Ref. SBDX011) were mounted on the unmanned submersible "Kaiko 7000 II" and submerged into the deep sea. Video footage shows the watches withstanding immense water pressure and operating at a depth of 3000m, far exceeding the specified depth of 1000m. JAMSTEC cooperated in this test and video recording.

　JAMSTEC is a national research and development agency that conducts activities to deepen our understanding of the global environment and life through marine research. In addition to research on understanding the global environment, utilizing marine resources, and investigating earthquakes and volcanic activity, JAMSTEC is also engaged in the operation of exploration vehicles and observation equipment, as well as technological development.

　JAMSTEC and Seiko have been collaborating since the 1980s. Furthermore, Seiko, with gratitude for the vast ocean, has been donating a portion of its sales to support JAMSTEC and contributing to environmental protection through marine research. As part of this support, Seiko has newly begun supporting JAMSTEC's Arctic research since 2025.

　The Marine Master 1968 Heritage JAMSTEC Collaboration Limited Edition model incorporates the relationship between Seiko and JAMSTEC, as well as Seiko's recent support for Arctic research.

A gradient dial inspired by the routes carved out by icebreakers on polar exploration missions.

　2026 marks a milestone year, as it will be the completion of "Mirai II," Japan's first Arctic research vessel equipped with icebreaking capabilities. Mirai II's participation in Arctic research is expected to enable data collection in ice-covered areas, leading to new and significant results.

　The dial of this collaborative model draws inspiration from Seiko's past support activities and the completion of the Mirai II, specifically from the routes created when icebreakers break through the ice of the Arctic Ocean. The entire dial features a pattern of sharp edges and random shapes, reminiscent of cracked ice spreading across the surface. The center of the dial is a deep blue, transitioning to white towards both sides in a gradient, representing the clear Arctic Ocean peeking through cracks in the ice.

　When I first saw the photos of this watch, I was impressed by the skillful use of gradation. Furthermore, when I held the actual watch in my hands, I was surprised by how three-dimensional and expressive it was, exceeding my expectations. In slightly dim lighting, the blue in the center is very dark, and the texture is almost invisible. However, when light hits the dial, the blue brightens, and the cracked ice-like texture behind it becomes more prominent. The gradation to white, along with the brightening of the color, makes the texture more clearly visible, and the way the watch's appearance changes is a distinctive feature.

　The bezel insert is made of blue ceramic, and its distinctive glossy texture gives it a modern and aesthetically pleasing look. The blue color is vibrant and matches the clear Arctic Ocean, which is the theme of this watch, creating a positive impression. Furthermore, the indices are sharp and have good contrast.

Sharp case design and comfortable fit.

　The case boasts a striking finish with sharp edges and polished, smooth surfaces. This high-quality polishing is the Zaratsu polishing technique that Seiko excels at, adding a compelling story to the watch. With a water resistance of 300m, it is suitable for serious diving.

　Before discussing the fit of this watch, I should mention that my wrist circumference is approximately 18cm, which is advantageous for fitting this large watch. When I tried it on, I found that despite its substantial weight, it was well-balanced and very comfortable to wear.

　Upon closer inspection, it appeared that the lugs offered a good fit with minimal lift from the wrist, and that the weight balance between the large case and the thick bracelet was well-maintained. Furthermore, the back of the case had a large bevel towards the sides, preventing interference with the back of the hand when worn. Even during a short period of wear, the case and crown did not dig into the back of my hand, and the gentle feel against the skin left a positive impression.

A long-awaited slim buckle with length adjustment function has been newly adopted.

　Another noteworthy feature regarding the wearing comfort is the newly developed buckle with length adjustment function. There is a switch on the back of the buckle for length adjustment, and when you hook your fingernail into it and pull, the fixing part moves in the direction that extends the total length of the bracelet. To shorten the bracelet length, no switch operation is required, and it can be shortened even when wearing it and closing the buckle. The ability to make fine adjustments while wearing it is a major advantage as it allows you to aim for a tight fit.

　This buckle with length adjustment is similar in size to a simple, compact buckle made of sheet metal. Large, thick buckles can come into contact with the desk during desk work, causing discomfort. Therefore, the compact size, especially the thin design, of this buckle contributes to greater satisfaction during daily use.

Equipped with the highly refined automatic movement Cal.8L45.

　The movement installed is the automatic Cal.8L45. This movement is the latest generation in Seiko's lineup and is also used in other models such as the King Seiko "VANAC". It boasts an impressive power reserve of approximately 72 hours and achieves the most stable accuracy among Seiko's current mechanical movements, with a daily variation of +10 to -5 seconds. Furthermore, it was developed with the intention of being used in a diver's watch, resulting in a robust construction, which provides peace of mind in everyday life.

A black dial model was also announced as part of the regular lineup.

　Alongside the announcement of the collaboration model with JAMSTEC, the Ref. HBF001J with a black dial also debuted as a regular model of the Marine Master 1968 Heritage. This model's dial features a rough, matte finish. Upon seeing this texture, I was reminded of the meters in sports cars and vintage industrial machinery, and felt it matched the stoic aesthetic of this timepiece. Not only is the collaboration limited edition model highly refined, but this model is also worth paying attention to.

The level of perfection befitting a flagship model is something you should definitely check out in stores.

　Through this in-depth analysis, we discovered that the Marine Master 1968 Heritage JAMSTEC Collaboration Limited Edition model features a case design that inherits the lineage of Seiko's diver's watches and a dial that reflects the collaboration with JAMSTEC, resulting in a finish that allows you to enjoy the background and worldview of this model. The exterior quality is also high, with Zaratsu polishing applied to the case and a ceramic bezel insert. In terms of performance, it is highly satisfying, with a 300m water resistance befitting a flagship model and the latest generation Cal.8L45 movement.

　The specifications—a case diameter of 42.6mm and a thickness of 14.1mm—might seem large and intimidating at first glance. However, the watch is crafted with comfort in mind, thanks to optimized case shape and weight balance, and the inclusion of a buckle with length adjustment. If you're interested in the design of this watch or are drawn to the history of Seiko diver's watches, we encourage you to try it on at a store.